Let the inclination of the plane be K and projectile is thrown making an angle 60 degree  with the incline.

Now, projectile makes an angle 60+K with the ground

[assume x axis along the plane and y axis perpendicular to the plane]

Vx= v cos 60                                                   
Vy=v sin 60                   

Also, resolve g

g x= g sinK
g y= g cosK

Now, solve for time of flight, range and H max