Tp/sqrt(Hs) has units of s/m^1/2 whereas 5.75 is dimensionless. You can not subtract apples from a dimensionless number. 5.75 must be in apples too.
Whats the point in asking the very same question twice??
Its already answered here -> https://community.ptc.com/t5/PTC-Mathcad/Mathcad-Prime-4-0-Need-the-the-solution-for-this-problem-AS...
If there still is something unclear to you then ask there.
Based on the time stamps I think this is probably a glitch in the forum's wonderful software.