How would you solve 5a^2 + 21a/2a^2 + 6a divided by a + 4/4a^2 divided by 5a^3 + 11a^2 + 2a/a + 3?
You have
(5a^2+21a)/(2a^2+6a) ÷ (a+4)/(4a^2) ÷ (5a^3+11a^2+2a)/(a+3)
a(5a+21)/2a(a+3) ÷ (a+4)/4a^2 ÷ a(5a+1)(a+2)/(a+3)
I suspect a typo: the 5a^2+21a ought to be 5a^2+a. If that is so, then we have
a(5a+1)/2a(a+3) ÷ (a+4)/4a^2 ÷ a(5a+1)(a+2)/(a+3)
a(5a+1)(4a^2)(a+3)
---------------------------
2a(a+3)(a+4)(a)(5a+1)
= 2a/(a+4)
If I got it wrong, just fix it and follow the same steps I illustrated.
Recall that multiplication and division are done left to right unless otherwise indicated by parentheses or obvious grouping.