We don't know the living room area and we are trying to find it so we use the variable x for the living room.
Living room = x
For the bathroom, 1/5 OF the area tells us to multiply 1/5 by x. Then it tells us the bathroom is 25 square feet less so it tells use to subtract 25. So we have an equation we can start to create like below.
bathroom = 1/5 * x - 25
It also tells use that the bathroom is 35 square feet so we can insert 35 into the bathroom section of our equation bathroom = 1/5 * x - 25
bathroom = 1/5 * x - 25
35 = 1/5 * x - 25
35 = 1/5x - 25
Now we just need to solve the equation 35 = 1/5x - 25
35 = 1/5x - 25
5 * 35 = 5(1/5x - 25)
175 = x - 125
175 + 125 = x - 125 + 125
300 = x + 0
x = 300
So the Living room area is 300 square feet.