Let's create expressions and equations to model this situation. Let Anthony's age be a.
"Jim is 3 times as old as his cousin, Anthony." Jim's age is 3a.
"The difference in their age is 18." 3a - a = 18
How old is Jim?
Let's solve the above equation for a to first find Anthony's age.
3a - a = 18
2a = 18
a = 9
Remember, Jim's age is represented by the expression 3a. Substitute Anthony's age, 9, into the expression to find Jim's age.
3a
3(9)
27
Answer:
Jim is 27 years old.