The answer: 6 cm
This is because sides PQ and RS are equal so set the two expressions equal
4x-1=3x+7
X=8
Then plug eight back into one of the expressions
4(8)-1=31
That means both sides PQ and RS are 31 cm, 62 cm are accounted for out of 72. Subtract 62 from 72 to find out how much is left
72-62=12
There are two sides left so divide by 2
12/2=6
