Answer:
12
Explanation:
Let :
x = number of Pizza's
y = number of burritos
x + y = 20 - - (1)
2.75x + 3.50y = 61 - - (2)
From (1) :
y = 20 - x
2.75x + 3.50(20 - x) = 61
2.75x + 70 - 3.50x = 61
-0.75x = 61 - 70
-0.75x = - 9
x = 9/0.75
x = 12
12 pizza slices