Francesca, who likes physics experiments, dangles her watch from a thin piece of string while the jetliner

Question:

Francesca, who likes physics experiments, dangles her watch from a thin piece of string while the jetliner she is in takes off from JFK Airport (Fig 4-58). She notices that the string make angle of 25o with respect to the vertical as the aircraft accelerates for takeoff, which takes about 18s. Estimate the takeoff speed of the aircraft.