Urgently solve

1).rate of change of area A of a circle of radious r with respect to time 't' is------------------------

a). 2nr, b). 2nr(dr/dt), c).nr^2(dr/dt), d). n(dr/dt).

2). the minimum assigned value of x for which the expression x^8/ 512 will be an integer?

a). -2, b).-3, c).+-3, d). +-4.