An explosion causes debris to rise vertically with an initial velocity of 160 feet per second. What is the speed of debris when the height is 300 feet?I am using the formula: -16t^2 + vot + h0 because the question is referring to feet.

The question is asking what v_final is, given that v_initial is at 300 feet. and v_initial is at 0 feet.  
We know there will be a constant downward acceleration of 32.15 ft/s^2.
 Use the following equation: 
 v_final^2 = v_initial^2 + 2ah
 v_final^2 = (160 ft/s)^2 + 2(-32.15 ft/s^2)(300 ft) = 6310 ft^2/s^2
 v_final = (6310 ft^2/s^2)^1/2 = 79.4 ft/s.