Yes, equation 3(-15) is basically saying that you are spending -15, 3 times and that those two numbers are being multiplied together which would give you the total cost of all the shirts you are buying. That being said, no purchase would be a negative value, this is most likely an error made when writing the question but the cost of each individual shirt should be $15 and not -$15. Therefore making the actual equation 3(15). We can even equal this to the variable C which would represent the total cost of the purchase and make it more of a real equation.
