How do I solve this motion problem using the given equations?

[faoltaem]

I have a problem from a practice physics exam:
The specifications for design of a playgroud slide say that a child should gain a speed of no more than 15m/s by sliding down the eqipment. How tall can the slide be?

these are the equations that we'll be given in our exam:
v_{x} = v_{0x} + a_{x}t
x = \frac{1}{2} (v_{0x} + v_{x})t
x = v_{0x}t + \frac{1}{2}a_{x}t^{2}
v_{x}^{2} = v_{0x}^{2} + 2a_{x}x

although i can work out the answer to the problem i had to look up a new equation because i couldn't work out how to do it with the equations that we were given, so i was wondering if it was possible to do it with one of them, so if you could tell me which one would work the best or if i should just start memorising some new equations, but here's what i did anyway:
v_{max} = 15m/s where g = -9.81m/s
v_{y}^{2} = -2g\Deltay
therefore \Deltay = \frac{v_{y}^{2}}{-2g} = \frac{15^{2}}{-9.81\times-2}
=11m

Thanks

 

[proasd]

I would work out the energy
gain in kinetic energy = loss in gravitational potential energy
(1/2)(m)(v^2) = (m)(g)(h)
simplifying you get
v^2 = 2(g)h
h = (121)/(2g)

 

[faoltaem]

thanks for that, i didn't even consider energy and those formulae are included too so no memorising

once again thanks a bunch