Calculating a Model Rocket's Speed and Altitude Using Acceleration of Gravity

[gragsur]

Homework Statement

A model rocket leaves the ground , heading straight up at 49 m/s
a) what is its maximum altitude?
b) what are its speed and altitude at 1,4 & 7 seconds

Homework Equations

v=v0 + at
x= x0 + 1/2 (v0 + v) t
x= x0 + v0t + 1/2 at^2
v^2=v0^2 +2a (x-x0)

The Attempt at a Solution

Am able to work out maximum altitude no problem , for some reason can't get my head around b) ?

 

[rl.bhat]

Use the formula
x = xo + volt - 1/2*g*t^2 and find x at given time t.