Step-by-step explanation:
the total surface area is the sum of the 5 individual areas in the surface :
2 triangle sides (left and right).
1 back rectangle side
1 rectangle floor
1 inclined rectangle front side
to get the length of the baseline (Hypotenuse) of the right-angled triangles on the side. we use Pythagoras
c² = a² + b²
where c is the Hypotenuse (the side opposite of the 90° angle).
c² = 3² + 4² = 9 + 16 = 25
c = 5
so, now, we have everything we need.
the area of a triangle side (since it is right-angled) :
4×3/2 = 6
2 sides, that makes 12
the area of the back side
6×3 = 18
the area of the floor
6×4 = 24
the area of the inclined front side
6×5 = 30
so, the total surface area is
12+18+24+30 = 84
