what is the longer easy method for 49b

Assign lengths, say an initial length of 100.

It helps to make calculations easier since you have actual numbers to deal with.

Remember that squares are also rectangles (a special case of rectangles), so you can let length = 100 and breadth = 100

New length is 120
New area is 15000

So new breadth is 125

This is a 25% increase from 100