As this is a parallelogram, the opposite sides are congruent. This means you can set their values equal to each other and solve algebraically for b.
5b - 7 = 10b - 27
-7 = 5b - 27
20 = 5b
4 = b
Plug 4 for b into the expression representing side YZ.
10b - 27
10(4) - 27
40 - 27
13
Answer:
YZ = 13 units