Answer:

Step-by-step explanation:
(Given)
Let's say the numbers are "a" and "b"
thus

set the derivative to 0, and check the critical points, there's only one anyway
and do a first-derivative test, to see if it's a maximum
We have two right triangles and three different rectangles.
The formula of an area of a right triangle:

l₁, l₂ - legs
We have l₁ = 20cm and l₂ = 21cm. Substitute:

The formula of an area of a rectangle:

l - length
w - width
We have:
rectangle #1: l = 22cm, w = 29cm

rectangle #2: l = 22cm, w = 21cm

rectangle #3: l = 22cm, w = 20cm

The total Surface Area of the triangular prism:

The answer for this question is 79 :)
Its the 2nd one becuase 2(-1)+2=0 witch is greater than -4.