HEL Tamara's little brother, Zane, likes to throw his basebal cap over the fence in their backyard. The motion of the cap is represented by the equation y= -3x + 9.1x, where x represents the number of seconds after Zane threw his cap in the air, and y represents the vertical height of the cap with respect to the ground in feet (assume that the cap is on the ground before Zane picks it up to throw it) a. How long is the cap in the air? How can you tell?