Suppose that the length of the rectangle is L cm and the width is W cm, then the area is 61 cm2 so
L W = 61
You also know that L is 1 cm more than 3 times W, that is L is 1 more than 3W. In other words
L = 3W + 1
Substituting this expression for L into the expression for the area I get
(3W + 1) W = 61
Solve for W.