A frictionless ramp is constructed so that it is at a 30 degree angle to the horizontal. It is 1.8 meters long and 0.9 meters high. A 4 kg block is released at the top of the ramp and slides down onto a frictionless horizontal surface where it hits and sticks to another block that has a mass of 5 kg. After the blocks travel some distance, the blocks come to a rough patch that has a coefficient of friction of 0.20 between the blocks and the rough surface. How far along the rough patch do the blocks go before stopping?