I am looking for an excel formula for this

In using transaction data to determine the current value of the subject property, it is important to recognize that general market conditions may have changed since a particular transaction occurred. Property A sold 22 months ago for $250,000 and Property B sold 16 months ago for $221,000. If the two properties are priced today at $299,000 and $245,000, respectively, what is the average monthly rate of increase that can be used to adjust comparable prices for changes in market conditions?