Which equation represents her dollar amounts spent

Question

Tickets Prices are

Adult $11

Child $7

Mary Spent $139 total on tickets. She bought 17 total tickets

Which Equation Represents Her Dollar Amounts Spent

a. 11a + 7c = 139

b. 18ac = 139

c. 7a +11c = 139

d. 139 +11c = 7a

Answer 1

11a + 7c = 139 , so option A is correct.

the second equation is a+c=17 ---> c = 17 - a

Substitution:

11a + 7(17 - a) = 139

11a + 119 - 7a = 139

4a + 119 = 139

4a = 20

a=5

5 adult and 12 child tickets cost

5*11 + 12*7 = 55 + 84 = 139