Let \( x \) be the number of months Brett has a membership.
Cost at Power Plus: \[ \text{Cost}_{\text{Power Plus}} = 21 + 34.17x \]
Cost at Heavy Hulk: The sign-up fee is halved, so it becomes: \[ \text{Cost}_{\text{Heavy Hulk}} = 16.75 + 34.42x \]
We need to find when these costs are equal: \[ 21 + 34.17x = 16.75 + 34.42x \]
Now, simplify this equation: \[ 21 - 16.75 = 34.42x - 34.17x \] \[ 4.25 = 0.25x \]
Now, solve for \( x \): \[ x = \frac{4.25}{0.25} = 17 \]
So, after 17 months, the cost of the memberships will be the same.
Answer: A. 17