Below is the beginning of a proof. Consider the proof and read the question carefully, then fill in the blank with the answer.

This proof is set up to start, with the given premises and the aim box filled out already. It also has Line $3$ filled in correctly. What wff should we write in the body of our proof on the next line?

$($Q $->$ R$),($S $->$ T$)|-($S $->($Q $->($R & T$)))$

$1(1)($Q $->$ R$)$ A

Aim: $($S $->($Q $->($R & T$))))$

$2(2)($S $->$ T$)$ A

$3(3)$ S A$/$CP $|-($Q $->($R & T$))))$