I GOT THIS ..
f(x)=x \sqrt{10-x}
f'(x)=(1)\sqrt{10-x} + (x)\frac{-1}{2\sqrt{10-x}}
=\frac{ 20-3x}{2{\sqrt{10-x}}}
editing..
got this wrong, misread your thing
If it's just for enjoyment then you could do it simultaneously with your studies but idk if you should start 8th grade now... ireckon concentrate on studies? if you think it's just too much stuff to handle then delay it till after exams :)