Please use the txhousing data frame to answer the following question:

You are interested in the cities "Dallas" and "Austin". In particular, you would like to know:

What is the average of the median house prices of houses that are in "Dallas" and "Austin" $?[-->$ all houses in "Dallas" and "Austin" are considered$]$

Remark: Ensure that you had previously removed all rows with missing values before conducting this calculation $($one of the initial questions$).$

Remark $2$: Provide your answer rounded to the closest integer.