Hello!
To solve this we will use substitutions and a system of equations where L= length and w=width.
128=2L+2w
L=8+3w
We will substitute L with what it says it equals in the second equation.
128=2(8+3w)+2w
128=16+8w
112=8w
14=w
Now we find the length in the second equation.
L=8+42
L=50
Now we check the length and width in the original equation.
128=100+28
128=128
The length is 50 cm, and the width is 14.
Hope this helps!