Answer:
4 cm
Explanation:
Perimeter of a parallelogram is 2b+2h=30 where b is base and h is height.
if AD is 3cm more than twice AB, then it's 3+2x where x is length of AB.
Input this into the perimeter equation: 2(3+2x)+2(x)=30
Simplify to get 6+6x=30
x=24/6=4
Answer is 4 cm.