I think you may have meant `5/sqrt(6)` so will answer here:
rationalize the denominator to get rid of the square root
`(5/sqrt(6)) times (sqrt(6)/sqrt(6))`
= `(5sqrt(6))/ 6`
If this is what you meant, solve as follows.
: Let the unknown =x
`therefore 5 sqrt(x)= 6`
`therefore sqrt(x) = 6/5` (square both sides)