Question 402710
total pizza cost = x
tip = y

since tip is 15% of total pizza cost, then
y = 0.15x

since total he has to give the delivery person is 13 dollars, then
x + y = 13

substituting for y
x + 0.15x = 13

this is the same as

1.15x = 13

x = 11.30

so total cost of pizza cannot be more than $11.30 

pizza base cost is $7.50 so he has left over for toppings

$11.30 MINUS $7.50 = $3.80

he has $3.80 to spend on toppings and each topping costs $1.25

3.80 divided by 1.25 = 3 remainder 0.05

he can buy up to three toppings