Two rectangles are similar. One has a length of 10 cm and a width of 8 cm, and the other has a width of 7 cm. Find the length of the second rectangle. Round to the nearest tenth if necessary.
If by similar you mean the area is the same then you find the area of the first.
The second triangle then is 7*x=80 which can be rewritten as x=80/7 => x=11.4.
7 is to 8 as x is to 10
7/8 = x/10
x = 7/8 * 10= 70/8 = 8 3/4 cm