Steps
1. Alan makes a table of length long and wide
2. Alan makes board for the table of length long and wide
3. Alan makes board loner than table so need to cut off,
Then
4. As we are having different denominators, we have to take LCD, by multiples of them
Therefore LCD is
5. As the denominator is changed the numerator also to be change by same number by multiplying
6. We can directly subtract numerators as we are having same denominators,
Then feet
Hence, Alan need to cut off the board is.