let

x = the age of Jamar, x>0

y = the age of Josh, y>0

Jamar is four times as old as Josh

x = 4y

In 20 years he will be as old as Josh is now

x + 20 = y

by solving the system of equations

x = 4y

x + 20 = y

we find the solutions

x = - 80/3

y = - 20/3

click here to see the step by step solution of the system of equations

we got negative solutions for the system of equations but the age of Josh and Jamar are positive numbers thus the problem has no solutions.