
with y equaling the total and x equaling the number if months
1.50c + 2.50a = 1100
c + a = 500
multiply the second equation by -1.50
1.50c + 2.50a = 1100
-1.50c - 1.50a = -7.50
These | | simple mean absolute value. Absolute value is simply the number positive, for example, the absolute value of -3 is simply 3