The energy that the student shoud use in order to climb the stairs is equal to its increase in gravitational potential energy:
[tex]W= \Delta U= mg \Delta h[/tex]
where m is the mass of the student, g the gravitational acceleration and [tex]\Delta h[/tex] the variation of height. Plugging numbers into the equation, we find
[tex]W=(60 kg)(9.81 m/s^2)(40 m)=23544 J[/tex]
The power required for the student to climb the stairs is equal to the work done divided by the time taken:
[tex]P= \frac{W}{t}= \frac{23544 J}{90 s}=262 W [/tex]
