Hello!
First:
write an equation.
5x + (7x+8) + (7x+2) = 143
now combine like terms
19x + 10 =143
now subtract 10 from both sides
19x = 133
divide 19 on both sides.
x = 7.
Are you done here? Nope, we need to find out what each side is, so lets plug in the number 7 for x.
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For the side 5(x)
5(7) = 35
This side is 35m
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For the side 7x + 2
7(7) + 2
49 + 2
51
This side is 51m
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For the side 7x + 8
7(7) + 8
49 + 8
57
This side is 57m.
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I hope this helps,
Have a great day!