at time zero, a skateboarder is moving along a ramp with an initial uphill speed of 8 meters per second. after traveling uphill a distance of 7.75 meters, the speed has decreased to 3.5 per second. The 'boarder keeps moving uphill they momentarily stop and reverse direction, returning to the initial position at the bottom of the ramp. label the uphill direction as positive.

how far uphill do they move before their speed decreases to 4 meters per second?