It costs $6 to buy a case and $3 to buy a screen protector. If the cost on a receipt for 8 items is $30, use substitution to see how many of each item were purchased?

Question

It costs $6 to buy a case and $3 to buy a screen protector. If the cost on a receipt for 8 items is $30, use substitution to see how many of each item were purchased?

Answer 1

Let x = number of cases and y = number of screen protectors.

x + y = 8

6x + 3y = 30

From the first equation, y = 8 - x.

So, 6x + 3(8 - x) = 30

6x + 24 - 3x = 30

3x = 6

So, x = 2 and y = 8 - x = 6.