How to estimate by rounding each number to the nearest ten

Enter the number of complex zeros for the polynomial function f(x) = x 4+ 5x² +6

Select the correct answer from the drop-down menu. subtracting 3xy^2 from 8xy^2 gives the same result as the expression. [tex]3xy ^{2} - 8xy ^{2} [/tex][tex] { - 7xy}^{2} - {2xy}^{2} [/tex][tex] {7xy}^{2} - {2xy}^{2} [/tex]

Me d is also an option but i couldn't get it in the picture