Check the signs in the first equation.
If you take g negative, h and V*sinθ are positive and the equation becomes
h = V*sinθ*t - 1/2*g*t^2. so the V will be
V=(4.92t^2 + 1.8)/0.8t
I have 2 formulas, derived from horizontal and vertical position;
V=(4.92t^2 - 1.8)/0.8t
The question was a projectile motion question to find what velocity a high jumper needed to be travelling at to make a jump of 1.8 metres that was √2 metres away launching at 53degrees. I worked out the 2 positions equations having the same V then created these 2 formulas from there. Not sure what to do from here.. Please help!