Answer:
13.5 = 9.5 + x
x=4
Explanation:
In this problem, the price of the baseball cap, which is $9.50, and a baseball, whose price is unknown (and therefore must be the variable), total $13.50. So, to set up the equation add the two prices and set them equal to the total, 9.5+x=13.5.
Then, using the subtraction property of equality subtract 9.5 from both sides. This means x=4, so the baseball cost 4 dollars.