First, you would need to create an equation to determine how much money he has earned thus far. 
($8 × 3) + ($10 × 2) 
Then, solve it. 
($8 × 3) + ($10 × 2) 
$24 + $20 = $44
Now, all you would need to do is subtract the money he has made so far from the money he needs. 
$45 - $44 = $1
Pete needs $1 more to buy a computer game. 
I hope this helps!