7. An elevator is travelling upward at constant speed \( v \). At a certain time, the elevator is at a height \( h_{1}=(8.67 \pm 0.05) \mathrm{m} \) above the ground floor of the building, and at a time of \( (2.57 \pm 0.05) \) s later, its height above the ground floor is \( h_{2}=(17.67 \pm 0.07) \mathrm{m} \). Determine the elevator's speed (and its absolute and percentage errors).