During a tunnel construction project, engineers used explosives to excavate partway into a mountain. because of time constraints and environmental concerns, they later used a tunnel boring machine (tbm) to excavate the rest of the tunnel. the table shows the length of the completed tunnel, y, after different numbers of days, x, since the tbm started working. number of days length of tunnel (feet) 0 225 5 350 20 725 30 975 55 1,600 the length of the completed tunnel can be calculated using what equation . if the project will be completed 86 days after the tbm was introduced, the length of the completed tunnel will be feet.