so far I have done:
$=\lim\limits_{h \to 0} \frac {(V(t+h)-V(t))} h$
$=\lim\limits_{h \to 0} \frac {(V(10+h)-V(10))} h$
$=\lim\limits_{h \to 0} 20(1-(100/(100+(10+h))-(20(1-(100/(100+(10^2)))))$
so I'm not sure how to finish and sorry I didn't know how to convert to the other form looking like the equation
$\frac {dv}{dt} = $$\lim_\limits {h\to 0} \dfrac {20(1 - \frac {100}{100+(t+h)^2}) - 20(1 - \frac {100}{100+t^2})}{h}\\ \lim_\limits {h\to 0}20 \dfrac {1 - \frac {100}{100+(t+h)^2} -1 + \frac {100}{100+t^2}}{h}\\ \lim_\limits {h\to 0}20 \dfrac {-\frac {100}{100+(t+h)^2} + \frac {100}{100+t^2}}{h}\\ \lim_\limits {h\to 0}2000 \dfrac {-\frac {1}{100+(t+h)^2} + \frac {1}{100+t^2}}{h}\\ \lim_\limits {h\to 0}2000 \dfrac {-(100+t^2)+(100+(t+h)^2)}{h(100+(t+h)^2)(100+t^2)}\\ \lim_\limits {h\to 0}2000 \dfrac {-100-t^2+100+t^2+2th +h^2)}{h(100+(t+h)^2)(100+t^2)}\\ \lim_\limits {h\to 0}2000 \dfrac {2th +h^2}{h(100+(t+h)^2)(100+t^2)}\\ \lim_\limits {h\to 0}2000 \dfrac {2t +h}{(100+(t+h)^2)(100+t^2)}\\ $
And let $h$ go to $0$
$\frac {dv}{dt} = 2000 \dfrac {2t }{(100+t^2)^2}$
and set $t=10$