Answer:
Value of r = 18
Explanation:
Make sure the base units are the same!!
This rectangular prism is known as a cuboid
Based on one of the three perspectives:
l = Length of rectangular base
= r cm
w = Width of rectangular base
= 11 cm
h = Height of prism or cuboid
= 18 cm
Surface area of cuboid = 2 × [l × w + w × h + h × l]
Apply BODMAS. Expand the parentheses starting from the innermost and making your way outwards. Then bring like terms and add them:
1440 = 2 × [(r × 11) + (11 × 18) + (18 × r)]
1440 = 2 × [11r + 198 + 18r]
1440 = 2 × [29r + 198]
Expand the last set of brackets by applying Distributive Law:
1440 = 58r + 396
r is to be isolated and made the subject of the equation:
58r = 1440 - 396
58r = 1044
r =
∴ r = Length of rectangular base = 18 cm