Given:
First side(A): 2B - 7
Second side(B): B
Third side(C): B + 4
Plug in values:
A + B + C = 80
2B - 7 + B + B + 4 = 80
If you look at the coefficients only, you can rewrite the equation like this:
2B + B + B - 7 + 4 = 80
This means that 4B - 7 + 4 = 80
=4B - 3 = 80
= 4B = 80 + 3
B = 83/4, so you can either write B as 83/4 or as 20.75.
Checking your work:
A: 2(20.75) - 7 = 34.5
B: 20.75
C: 4 + 20.75 = 24.75
34.5 + 20.75 + 24.75 = 80cm.
Hope this helped.
