In British English (which I know is different):
842 = eight hundred and forty-two
6,554 = six thousand, five hundred and fifty-four
152,600 = one hundred and fifty-two thousand, six hundred
1.4 million = one point four million (1,400,000 = one million, four hundred thousand).
Don't forget to use , instead of . other than for the decimal point because actually:
6.554 = six point five five four
152.600 = one hundred and fifty-two point six nought nought