Can someone plz help me with this one problem!!!

Answer:
v = 9 m
Step-by-step explanation:
the formula for the perimeter is P = 2W + 2L.
Here the perimeter is 42 m = 2(12 m) + 2v. Solving for 2v, we get:
42 m - 24 m = 2v, or
v = 21 m - 12 m, or
v = 9 m