Answer: $60.00
Step-by-step explanation: First the solution: (Start form the end!!) $40.00 (the ending total) minus the $10.00 he added on, $40-$10=$30 which is half of the original total so now you have to multiply by two to get the starting balance ($60.00)!
Now for the inequality, since we don't know the beginning balance of the gift card that will be our variable.
g
Then, since he spent half of this buying coffee we would have to split our variable in half.
g/2
After that, Peter added an additional $10.00 to said gift card.
g/2 + 10 = 40
Going off of that the final inequality would be $60.00 = g/2 + 10 = 40
BAMM!! GOOD LUCK IN MATH CLASS!!!