Answer:
   side lengths are 6, 12, 12, 9, 9
Step-by-step explanation:
The perimeter is the sum of the lengths of the sides:
   x + 2x + 2x + (x+3) + (x+3) = 48
   7x +6 = 48 . . . . collect terms
   7x = 42 . . . . . . .subtract 6
   x = 6 . . . . . . . . . divide by 7
Substitute this value into the expressions for the side lengths:
   x = 6
   2x = 12
   x+3 = 9
The side lengths are 6, 12, 12, 9, 9.