pls help

An aircraft has a liftoff speed of v = 33m/s. What minimum acceleration a does this require if the aircraft is to be airborne after a takeoff run of s = 240m? Please help I really don't understand this!!!!!

$s=\frac{a}{2}\times t^{2}$

$s=v \times t$     

$t=\frac{s}{v}=\sqrt{\frac{2s}{a} }$

$\frac{s^{2} }{v^{2}}=\frac{2s}{a}$ 

$a= \frac{2v^{2} }{s}$

$a=\frac{2\times 33^{2}m^{2} }{240m\times s^2}$

$a=9.075\frac{m }{s^{2} }$

The aircraft has to start with an acceleration of at least $9.075\frac{m }{s^{2} }$

asinus :- )  !