if f(x)=2^x , and a and b are any positive numbers, then f(a+b) is equivalent to f(a)*f(b) , explain why

The path traveled by a bottlenose dolphin as it jumps out of water is modeled by the equation y=-0.4+3x, where t is the height above water and x is the horizontal distance in feet. if a beam of light is shone upward at an angle modeled by the equation x+y=10, at what height from the waters surface will the beam of light hit the dolphin