Well you cant really answer this without "P" being equal to a number unless you want an equation as an answer but ill try to explain.
OK so it says twice the difference of "P" and 10 that just means do P-10 and then times that number by 2. For example lets say "P" equaled 15 it would be 15-10 which is 5 and times that by 2 which is 10. Get it?