A perimeter is all of the sides added together. In this problem, you have 6 sides, so you would take all 6 of those measurements and add them together. The perimeter of this shape would be 32+b. Reason why I said plus b is because you don't know what b is, therfore you would add it to the rest since that is what we did with the rest of the numbers. Make sure not to put 32b because then that would be multiplying the two and that isn't what you want.
I hope this helps!