Question 1036123
W1/L1 = W2/L2 therefore 7.5/12.5 =3/L2 Therefore L2 = 5

One way to solve this problem is to think about the wide of the first rectangle divided by the length of the first rectangle is supposed to be the same as the width of the second triangle divided by the lengths of the second rectangle. 
After setting the formula as appears above we can find the length of the second rectangle which is 5 centimeters.