If $f(x,y)=x{y}^2{5}^{-x-y},$ then which of the following is closest to $f_y(-5,6)$

a$)45\mathrm{.}9$

b$)65\mathrm{.}1$

c$)-60\mathrm{.}3$

d$)-43\mathrm{.}3$