Power of rider = Force times Velocity = $80\cdot 9.8\sin(\theta) \cdot \frac{10}{14}\cdot 10 = 5600\sin(\theta)$ watts
Going up the incline $5600\sin(\theta) = 80\cdot9.8\sin(\theta)v + 80\cdot9.8\sin(\theta)\cdot \frac{10}{14}v$
$5600 = 80\cdot 9.8\cdot \frac{24}{14}v$
$v = \frac{5600\cdot 14}{80\cdot 9.8\cdot 24}$
$v = 4.167$ m/s