Answer:
Since the pendulum moves from side to side in 1 sec, the length of the arc covered by the pendulum in an oscillation will be the length travelled in 1 sec
From trigonometry, we know the relation:
Θ(in radians) = l / r (where r is the length of the pendulum and l is the length of arc travelled)
But first, we need to convert 20 degrees to radians
20 degrees = π/9 radians
r = 7 feet
Now, plugging these values in the equation:
π / 9 = l / 7
l = 7π / 9 feet
l = 2.44 feet (approx)
