A rectangular animal pen with the area 1200m has one sidealong a barn. The other three sides are enclosed by a 100m fencing. Find the dimensions of the pen.

I want to believe that the sides of the rectangle are 60x20x60x20 having one of the sides that are 60m along the barn making a 100m fence for the other 3 sides and a total area of 1200m (60mx20m)