Bayesian Probability II

Bayes law is based on the idea that prior knowledge about A $($e$.$g$.$ whether or not a plant is a tree$),$ provides information about B $($e$.$g$.$ whether or not a plant lives indoors$).$

The formula for Bayes law is:

Use this formula to solve the following problem: In a shop, people can take chewing gum from a dispenser on the right, or the left. The dispenser on the right has $7$ packets of mint gum, and $3$ packets of fruit gum, and the dispenser on the left has $7$ packets of mint gum and $7$ packets of fruit gum.

Someone buys a packet of mint gum $-$ what is the probability that they took this packet from the right dispenser?