A girl has an age of x years. Her grandfather is aged y years. Write an expression for: 

a. Their combined age.

b. The difference between their ages. 

c. The grandfather’s age 10 years ago. 

d. The girl’s age when she is twice as old as she is now.

e. Their combined age in 5 years’ time.

f. The difference between their ages in 5 years’ time.

g. The grandfather’s age when the girl is twice the age that she is now.