How do you do this?

Answer:
[tex]210cm^{2}[/tex]
Step-by-step explanation:
The surface area is equal to 2(ab+ac+bc)
where ab, ac and bc are the lengths of the three sides given
Height (a) = 5cm
width(b) = 80mm = 8cm
Depth (c) = 5cm
2((5*8)+(5*5)+(8*5))
2(40+25+40)
2(105)
210