Answer:
It would need to be 324.23 feet high (not reasonable)
Step-by-step explanation:
If you plug it into the pendulum formula given T = 2 π √(L/32), all you would have to do is set T=20 and solve for L
You would end up getting 3200/(π²)
this is equal to 324.227
This was the formula given to me by the assignment, not sure if it is the same on yours. Good luck! ;)