So this is asking how many balls you have to add to 106 to get the total of 250. This is the equation 106 + x = 250, where x is the unknown number of balls. If you subtract 106 from 250, all you have left is the unknown section, so the equation x = 250 - 106 is how to solve for the unknown. This equals 144, which is the solution, since 250 - 106 = 144.
The solution is 144.
