Jillian is selling boxes of cookies to raise money for her basketball team. the 10 oz. box costs $3.50, while the 16 oz. box costs $5.00. at the end of one week, she collected $97.50, selling a total of 24 boxes. the system of equations that models her sales is below. x+ y= 24 3.50x + 5.00y = 97.50 solve the system of equations. how many 10 oz. boxes were sold?
a. 6
b. 9
c. 12
d. 15

we have to solve simultaneous equations.
                                                                     
x = 10 oz. boxes
                                                                     
y = 16 oz. boxes
                                                                               
simultaneous equations
                                                                     
x + y = 24 ---1)
                                                                     
3.50x + 5.00y = 97.50 2)
                                                                   
to solve for x we need to eliminate y, therefore we have to multiply 1st equation by 5
                                                                   
5x + 5y = 120 --3)
                                                                   
subtract 3) - 2)
                                                                   
5x - 3.50x = 120 - 97.50
                                                                   
1.50x = 22.5 x = 15
                                                                     
number of 10 oz. boxes are 15. answer is d.15