Solve, really need can't fail.

in the figure above, abc is similar to xyz. if the length of side ab is 15 units, the length of side bc is 40 units, and the length of side yz is 8 units, what is the length of side xy?

a.5 units
b.3 units
c.4 units
d.1 units

Well, we know that if two polygons are similar, then their sides are proportional. Therefore, side AB is similar to side XY and side BC is similar to side YZ. This means that AB / XY = BC / YZ. From here, plug in values: 15 / XY = 40 / 8. This can be simplified to 15 / XY = 5. Multiply both sides by XY to get it out of the denominator: 15 = 5XY and then divide each side by 5. 3 = XY. This means that the answer is B, or 3 units. To check the answer, put it back into the original equation and make sure it works out. 

Hope this helped!!! :)