Question

What is the width of the mat?

Answer 1

If you want the strip around the mat:

x=strip of mat

2(20+2x)+2(15+2x)=102
Distribute
40+4x+30+4x=102
Combine like terms
70+8x=102
Subtract 70
8x=32
Divide by 8
x=4

If you want the whole width of the mat:

w=15+x
w=15+2*4
w=23