SOLUTION: The surface area of a cuboid is 102cm square. Height is 3cm, width is 4.5cm. What is the length marked x?

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Question 168282: The surface area of a cuboid is 102cm square. Height is 3cm, width is 4.5cm. What is the length marked x?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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The surface area of a cuboid is 102cm square. Height is 3cm, width is 4.5cm. What is the length marked x?
:
The surface area of a rectangle which is what a cuboid is:
2LW + 2Lh + 2Wh = S.A.
:
Substitute x for L; 3 for h; 4.5 for W, 102 for SA:
2(4.5x) + 2(3x) + 2(4.5*3) = 102
:
9x + 6x + 27 = 102
:
15x = 102 - 27
:
15x = 75
x = 75%2F15
x = 5 cm is the length
:
:
Check in the S.A. equation
2(4.5*5) + 2(3*5) + 2(4.5*3) =
2(22.5) + 2(15) 2(13.5) =
45 + 30 + 27 = 102