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:

Can we get a clearer pic?
Answer:
it doesn't
Step-by-step explanation:
hehe, try again
Solving for x
x=3/8m-5/4,m
Solving for m
m=10/3+8/3x,x