'That' refers to 'the $ amount of loan repayments and imports,' from the first quarter, in this case. I don't know the technical term for this, but 'that' is being used as placeholder...i.e. more concisely expressing the following: '...to cover loan repayments and imports that will probably come to twice  / the $ amount of loan repayments and imports/ from the first quarter of the year. If you're a math person, 'that' in this case is like X, where X = the amount in $ of loan repayments and imports.

"That" is a pronoun which refers to "$3.5bn." Loan repayments and imports will probably come to more than 2 x $3.5bn, or more than $7bn.

loan repayment