To solve proportions it helps to understand how to set up ratios.  A ratio is basically just like a fraction with one number on top of another number.  A proportion is two ratios that are equal to one another.  For example the fraction 1/2 = 2/4.  When 2/4 is simplified, it equals 1/2.  That means they are proportional.  A quick way to see if two ratios are proportional is to multiply the numbers that are diagonal from one another (cross products) and see if the answer are equal.  If the two answers are equal, the ratios are proportional.

The first step is to cross multiply (which we call "cross products"). Then set your cross products equal to one another.

Solve the equation.

And, that's all there is to it.

For some more help on proportions check this out: 4-1 Proportions