Arectangle has a length of x inches and a width 3 inches less than the length. if the dimensions were doubled , what would be the area of the new rectangle in terms of x ?

Original length: x
original width; x-3
original area: x(x-3)
when the dimensions doubles, that is, increase by a factor of 2, the area increase by 2²
4[x(x-3)]
4x(x-3)=4x²-12x

you can also do it this way:
original length: x        doubled: 2x
original width; x-3      doubled: 2(x-3)
new area: 2x[2(x-3)]= 4x²-12x