first you add the common variables so... 16x - 4x = 12x
and 58.75 - 25 = 33.75
And 1 the most common mistake is that people add 25 and 58.75. The reason you don't do this is because the two equations are subtracting or trying to find the difference regardless of whether the numbers are positive or not. Although if they were negative numbers you would be adding.
