Answer:
13 seconds.
Step-by-step explanation:
Given

Required
Determine a reasonable solution for t
To do this, we equate h to 0.
becomes

Divide through by -4.9

Reorder the expression

Split
or 
This gives:
or 
But time can't be negative, So:

Answer:
2
Step-by-step explanation:
20/2 = 10
4/2 = 2
Answer:
24
Step-by-step explanation:
2/5 = 40%
40% of 60 = 24