Question

by substitution method answer fast

Answer 1

jacob's age be x
son's age be y
after 5 years
                    (x+5) = 3(y+5)
                      x = 10+3y
before 5 years 
                       (x-5) = 7(y-5)
                        x - 7y = -30
substituting x = 10+3y in x-7y = -30
                     10+3y-7y = -30
                     10-4y = -30
                      y = 10
so x = 40