Question 764006
Large pizzas = x
Small pizzas = y
x + y = 34...1
18x + 11y = 479...2
Multiply 1 by 11
11x + 11y = 374...3
18x + 11y = 479...2
Subtract (3) from (2)
7x        = 105
 x        = 15
Substitute x = 15 into (1)
x + y = 34
15 + y = 34
     y = 34 - 15
     y = 19
So, 15 large and 19 small pizzas were sold.
Hope this helps.
:-)