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: You divide the top row by itself and you multiply the top by 2 each time.
Step-by-step explanation: Multiply 72 by 2 each time on top and the bottom row just simply add 1.
Sorry if it is wrong but i hope it helps!
18-7n+1= -9
You just have to ignore the first thing it asks for, and then write out what it's saying. Since it's asking for the difference, you have to subtract what it tells you to. In this case they are asking for you to subtract 7 times a number from 18 which is the same as writing 18-7n. Then, go back to the first thing it asks for and that wants you to add one. You now have this: 18-7n+1. Now all you have to do is set it equal to whatever it asks you for, which is -9. The final product should look like this:
18-7n+1= -9
I hope this helps and if you could let me know if I helped, that would be greatly appreciated!
Answer:
-15
Step-by-step explanation:
the new temperature since it went down
-12-3= -15