Equation of a line is given by y = mx + b; where m is the slope and b is the y-intercept.
In the given equation, y = -13x + 56k; b = -10
56k = -10
k = -10/56 = -5/28
8+6=14, 14+6=20 so Jamal must be 3 , cause both ages are added together to make 20 then whatever is left is Jamal's age !!
