we know that
the dimensions of the first garden are------> 5 ft x 3 ft
perimeter first garden=2*[5+3]-----> 16 ft
the dimensions of the second garden are---> (5*2) ft x (3*2) ft
10 ft x 6 ft
perimeter second garden=2*[10+6]-----> 32 ft
so
The answer is
32