Question 118542
Let x, y and z be the three sides. From the information given, you know:

Equation#1: y=x+5
Equation#2: z=2x-3
Equation#3: x+y+z=42

You have three equations and three unknowns. Anytime you have at least as many equations as you have unknowns, you can solve the problem!

Use substitution methods like this to do it:
First, substitute the expressions for x and y in Equations #1 and #2 into Equation #3. You get:
{{{x+x+5+2x-3=42}}}
Solve for x:
{{{4x+2=42}}}
{{{4x=40}}}
{{{highlight(x=10)}}}
So you have one side... plug this value of x into Equations #1 and Equation #2, solve for y and z respectively, and you are done. I will leave that part to you.
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Good Luck,
tutor_paul@yahoo.com