How do I solve for the distance?

Mendoza Problem 1 Block 1 of mass mi slides from rest along a frictionless ramp from height h = 2.5 m and collides with block 2 of mass m2 = 3m, initially at rest. After the elastic collision, one of the blocks slides into a region where the coefficient of kinetic friction is 0.5 and comes to a stop in distance D within that region. What is the value of D? mi Frictionless Region with friction h m2