Hey!
Let's write the problem,

Multiply both sides by

in order to undo the fraction.


Let's switch sides so that we end up with

on the left side.

Divide both sides by

.

Our final answer would be,

Thanks!
-TetraFish
1.08 km^2 you get this by converting 900 meters to .9 km and then just multiply the 2 numbers together to get the area
C = d × pi
C = 6 × 3.14
C = 18.84
$21.50(40) + $31.88 (62-40)
$21.50(40) + $31.88(22)
$860 + $701.36
$1561.36
To find the number of half lives divide the total number of days by the number of days for 1 half live:
1104 / 138 = 8
There are 8 half lives.
To find the total amount left multiply the starting amount by 1/2 to the 8th power:
38 * 0.5^8 = 0.148 = 0.15 grams
The answer is the last one.