Test 4 Section 3 - #18 (page 585)

Big time plug-in here. Say x = 10, and z = 2. So the first shirt will cost $10, and each shirt after that will cost $10 - $2 = $8. Now say the customer buys n = 5 shirts. Those shirts would cost

$10 for the first one

+ $8 for the second

+ $8 for the third

+ $8 for the fourth

+ $8 for the fifth

= $42 

So we're looking for the answer that gives us 42 when we plug in the number we chose above.

(A) x + (n - 1)(x - z)


We can translate that to
10 + (5 - 1)(10 - 2) = 10 + (4)(8) = 42.

That's our answer! Make sure, when you plug in, that you try the other answers too to make sure they don't work. In this case they don't, so we're done.