> I know that when we want to say we do someone a favor or we give someone something, we use "ageru". This is wrong. "Ageru" means only to give someone something or raise something. For the tranlsation "I'll do it right away for you, sir" is "sugu/tadachi ni itashimasu", but the how expression would look like depends on the verb, what "do" actually does. In Japanese we would never say "Anata no tame ni" (for you) in any context. It sounds like I want something from the person in return. Never say that.

So, I think we should be careful about adding あげる to a verb when you're talking to somebody DIRECTLY. If you are to talk about above incident with your friends or your boss or anybody, you can say like this: Today I saw someone at lost, so I went to the station with him/her. きょう、みちに　まよっているひとが　いたから、　えきに　いっしょに　いってあげました。 So, when you explains your action to a THIRD PERSON, it is definitely OK to use あげる. Then, what kind of situation is where さしあげる can properly be used? Here it is: ((You are working at a reception desk at a hotel. A guest was asking a chief receptionist how to get to a station. He was busy at the moment. So, he told YOU to take the guest to the station.)) おきゃくさまを　えきに　つれていって　さしあげなさい／さしあげて。 Then, you say to the guest that you will take him/her to the station. それでは、えきまで　おつれします。 Go back to your original question. The Japanese sentence would be like this as other persons have already written here. ただちに（すぐに）いたします。 I hope this will help you sort things out.

It depends on situations, as a spoken word: a hotel staff say to the guest: watakushi(=watashi) ga itasimasyouka? to your boss (have friendly relation): watashi ga yarimasyouka? or watashiga yarimasu. to starangers who need help: tetsudaimasyouka? watasi ga yarimasyouka? to close friends : yatte ageyouka? yarouka? to the children: yatte ageru. yatte ageyouka? Normally question style is more gentle and friendly. "sashiageru" is not wrong but very very formalway to say ageru, and not using normal situation desu.

It depends on situations, as a spoken word: a hotel man say to the guest: watakushi(=watashi) ga itasimasyouka? tell to your

The humble version of "ageru" is "sashiageru": https://en.m.wikipedia.org/wiki/Honorific_speech_in_Japanese