$f(x^2) =x^3 (2+x^2),$$f(x^2)= \int \limits_0^{x^3} f(t) dt,$ find $f(8)=?$

Question

$$\begin {array} {1 1} (a)\;8 \\ (b)\;9 \\ (c)\;10 \\ (d)\;12 \end {array}$$