Answer:

Step-by-step explanation:
If the initial number is n, one less than n is n - 1, and one more than n is n + 1. so we have:

At first I thought this answer was too easy, so I tried for n is 6.

This is really cool! Hope this helps!
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
Its the first one for all three of the questions
It has 3 zeroes which are

Hope this helped!
~Just a girl in love with Shawn Mendes