### Home > A2C > Chapter 2 > Lesson 2.1.3 > Problem 2-39

2-39.

Continue adding 12 to find months 2-5.

See part (a). (Continue until month twelve.)

Remember that the initial amount was 120 stamps and the rate is 12 stamps per month.

Use these values to make an equation.

t(*n*) = 120 +12*n*

Substitute 500 for t(*n*).

500 = 120 + 12*n*

Solve for *n*.

Lona will not be able to fill her book exactly, with no leftover stamps, because when the equation is solved for *n*, the result is a mixed number. It will be filled in 32 months.