Melanie is tiling her shower with blue and white square tiles. She needs enough tiles to cover 72 square feet. Each tile is the same size. To get the look that she wants, Melanie will use x blue tiles and y white tiles per square foot. Write an expression in terms of x and y that represents the total number of tiles needed per square foot.

Let Ted be x.

Ed is 7 years older =  x  + 7

Ed = (3/4)Ted

(x + 7) = (3/4)x

x + 7 = 3x/4

x - 3x/4 = -7

x/4 = -7

x = -28,           Ted = -28 years

(x + 7) = -28 + 7 = -21,      Ed = -21 years.

Goodness. We had negative numbers for the ages, well does that make sense?  No it doesn't.

Our answer is correct. But the sense in the question is lacking. The question has been wrongly set.

We might assume negative ages to mean before they came into the world, before birth!