help me please i have to show work.i will give you brainliest.

Answer:
A = 142
Step-by-step explanation:
The formula for surface area of a rectangular prism is 2(wl+hl+hw), with w = width, l=length, and h = height. If you plug in the measurements of the prism, you get:
A = 2((3*7)+(5*7)+(5*3))
Simplify inside the parentheses:
A = 2(21+35+15)
Simplify further:
A = 2(71)
Multiply:
A = 142