7. Two smooth spheres \(A\) and \(B\), of equal radius and masses \(9 m\) and \(4 m\) respectively, are moving towards each other along a straight line with speeds \(4 \mathrm {~ms} ^ { - 1 }\) and \(6 \mathrm {~ms} ^ { - 1 }\) respectively. They collide, after which the direction of motion of \(A\) remains unchanged.

1. Show that the speed of \(B\) after the impact cannot be more than \(3 \mathrm {~ms} ^ { - 1 }\). The coefficient of restitution between \(A\) and \(B\) is \(e\).
2. Show that \(e < \frac { 3 } { 10 }\).
3. Find the speeds of \(A\) and \(B\) after the impact in the case when \(e = 0\).