Answer: 16 single crust apple pies and double crust apple pies were sold.
Explanation:
Let x represent the number of single crust apple pies sold on a Friday.
Let y represent the number of double crust apple pies sold on a Friday.
The total number of pies sold on a busy Friday was 36. This means that
x + y = 36
Grandma's bakery sells single crust apple pies for $6.99 in double crust cherry pies for $10.99. The total amount that was collected that Friday was $331.64. This means that
6.99x + 10.99y = 331.74- - - ---- - - - -1
Substituting x = 36 - y into equation 1, it becomes
6.99(36 - y) + 10.99y = 331.74
251.64 - 6.99y + 10.98y = 331. 74 - 3 31.74
251.64 - 331.74
4y = 80
y = 80/4 = 20
x = 36 - y i= 36 - 20
x = 16