For projectile on a plane inclined at angle alpha:

Set axes along and perpendicular to the incline:

• Along incline: a_x' = -g*sin(alpha) [deceleration going up]
• Perpendicular to incline: a_y' = -g*cos(alpha)

If launched at angle beta to the incline with speed u:

• u_x' = ucos(beta), u_y' = usin(beta)
• Time of flight: T = 2usin(beta)/(gcos(alpha))
• Range along incline: R = 2u^2*sin(beta)cos(alpha+beta)/(gcos^2(alpha))
• Max range when beta = (pi/4 - alpha/2), i.e., bisect angle between incline and vertical

JEE trick: Range up the incline != range down the incline for the same launch angle.