She's wrong. If you have two squares, with side
and
with side
, it's not true that the sum of their areas is equivalent to the area of a square
with side
.
So, there's no point in summing the two sides. Instead, you have to compute the areas of the two squares and then sum them up.
So, the area of the first square is , and the area of the second square is
.
Add these two numbers and you'll get how many squared meters of carpet she'll need.