8 cm
The formula to find the surface area of a rectangular prism is SA = 2ab + 2bc + 2ac, where a, b, and c all equal one side of the prism.
To solve this, plug in the value for surface area and the values of the known sides. let’s say a = 3cm and b =5cm and c = y cm. It doesn’t matter with value gets assigned to which letter.
SA = 2ab + 2bc + 2ac
158 = 2(3)(5) + 2(5)(y) + 2(3)(y)
158 = 30 + 10y + 6y
158 = 30 + 16y
128 = 16y
y = 8 cm