jmc

The area of a rectangle is given by the formula length times width. Karl's garden is $20\times 45=900$ square feet and Makenna's garden is $25\times 40=1000$ square feet. Since $1000>900,$ Makenna's garden is larger by $1000-900=100$ square feet. $\Rightarrow \boxed{\text{Makenna’s garden is larger by 100 square feet.}}$