Solve this system of equations using substitution.
a+b+c=180
b=3a
c=5a

The first thing to do is to substitute the b and c. The equation will look like this, a+3a+5a=180. Then you must add the a's all together because they are all the same, remember that "a" represents 1. It will look like this in plain 1 + 3 + 5. Then the equation is 9a = 180. to get the "a" you must eliminate or divide the equation into 9 and it will look like this, 9a = 180  Then the answer will be a = 20
                                                   9        9