What s the total cost of a $12.50 item plus 7% tax? is the question how do you find the answer?

So percent means parts out of 100 so
7%=7/100=0.7/10=0.07/1=0.07

so we want to find 12.50 +7% of 12.50

'of' can be translated as multiply

12.50+(0.07 times 12.5)=12.5+0.88=13.38

the total cost is 13.38

a shortcut is if you want to find cost+tax then
cost=1 and tax=0.07 so 1+0.07=1.07 so to find cost, just multply by 1.07

Y=x because the question is undefined