A pizza parlor sells pizza slices for $ 3 each and calzones for $ 4 each. A group of friends spent $ 51 on pizza slices and calzones at the parlor. If they bought 6 calzones, how many pizza slices did they buy?

The correct answer is: 9

HINT :- total amount spent = total cost of pizza slices + total cost of calzones
Given, each pizza slice costs $ 3 and each calzone costs $ 4
no. of calzones bought is 6 and total amount spent is $ 51
Let no. of pizza slices be x.
total amount spent = total cost of pizza slices + total cost of calzones
Step 1:find total cost of pizza slices
total cost of pizza calzones = cost of each calzone × no. of calzones bought
=  
Step 2: find total cost of pizza slices
total cost of pizza slices = cost of each pizza slice × no. of pizza slices bought
=
$51 = $24 + $ 3x

No. of pizza slices bought is 9.