Length of the stem at time 0 is 20 cm. The arithmetic growth rate is 30 cm per day. What is the length of the stem at the end of the 7^ th day?

Length of the stem at time $\displaystyle 0$ is $\displaystyle 20$ cm. The arithmetic growth rate is $\displaystyle 30$ cm per day. What is the length of the stem at the end of the $\displaystyle 7^{\text {th }}$ day ?