let = time (in sec) the grenade is a projectile

position of the enemy car in meters ...

position of the projectile ...

... where is the x-component of grenade's initial velocity

since the idea is for the projectile and enemy car to be at the same place at the same time ...

in the y-direction, the projectile's total displacement is zero ...

... where is the y-component of the grenade's initial velocity.

solving for ...

since the launch angle is , , so .

... substitute for in the equal position equations and solve for