Thank you i advance :-)
Hint: Take the -dS/Q^2 term to the RHS side and then take the reciprocal of both sides which will give Q^2/dS = blah. After this you multiply both sides by dS and take the square root.
Show us your attempts so we can guide you through them.
I would move the fraction with Q^2 to the right hand side of the equation to start.
Combine fractions on the left
Divide both terms in the parenthesis by p
Invert both sides
Multiply by dS
Extract the root
Question: What is the subscript on h for?