Proof Writing & Problem Solving · Easy problem

To prove "if $d \mid a$ and $d \mid b$, then $d \mid 3a - 2b$", write $a = dk$ and $b = dl$ for integers $k, l$; then $3a - 2b = d(3k - 2l)$. For $d = 7$, $a = 35$, $b = 21$, what is the integer $3k - 2l$?