Question b) Trying to solve for the partial derivative for theta with respect to r is giving me an aneurism, someone please help. Have exam in 3 hours

We got this assignment and it's due in 20 minutes, but none of us can seem to solve it. Even just the process or steps to solve it is ok. I just need some backbone.

I’m 20 and was taken out of traditional schooling in 6th grade for medical reasons. I’m currently rebuilding my academics, especially math, through an intensive remedial course during my gap year. After that, I plan to start community college and eventually apply to transfer to a strong university.
I’m planning to take the SAT in about two years, and my goal is 1500+. I know that’s ambitious given my starting point, but I’m committed to putting in the work.
How would you recommend preparing over that time? Should I focus entirely on my foundations for now, or introduce SAT-specific practice along the way? I’d especially love to hear from anyone who started with significant math gaps and eventually scored well. What helped you most?