Rock of Ages

You will find SkeeBoulder in the single-player menu. SkeeBoulder plays similar to story mode but instead you will try to rack up points through the board by hitting easels and items and instead of breaking gates at the end you will find a Skee style board. The goal as suggested by the achievement image is to hit a x6 multiplier.
The x6 multipliers are located in the top left and right of the board. What you need to do is hit the ramp with some speed and aim at the corners, it is quite simple as long as you have some speed. Hit 'A' as you are going up the ramp. The main thing to remember is that if you get stuck or overshoot you can jump with 'A' and then angle yourself into the pocket.

Video credit to thecontrolleronline

Can also be done in multiplayer (local or online). Pick SkeeBoulder, get your rock to the bottom of the course and jump either slightly left or right as the X6 multipliers are up top on either side. If you missed the initial jump, just roll up the target and jump in.

This one is not hard at all. When you reach the bottom of the level and hit the ramp for the skeeball, simply jump so you get into the ring. From there, you can just roll your way up to the top. Get above the x6 multiplier, then just press "a" to jump up and into the hole. You really don't need much aim or anything to do this one.