Answer:
The function that represents the mass of the sample after t days is
.
The percentage rate of change per hour is of -2.46%.
Step-by-step explanation:
Exponential amount of decay:
The exponential amount of decay for an amount of a substance after t days is given by:

In which A(0) is the initial amount, and r is the decay rate, as a decimal.
Element X is a radioactive isotope such that its mass decreases by 59% every day. The experiments starts out with 390 grams of Element X.
This means, respectively, that 
So



The function that represents the mass of the sample after t days is
.
Hourly rate of change:
Decreases by 59% every day, which means that for 24 hours, the rate of change is of -59%. So
-59%/24 = -2.46%
The percentage rate of change per hour is of -2.46%.
Okay. So first you subtract 2x from each side. That will give you 4y= -2x+18 (you want to get y by itself). Then you divide both sides by 4. It should equal> y= 1/2x +9/2
Using elimination method. Using substitution will cause some fraction problems.
c- child tickets
a- adult tickets
4a + 7c = $83
5a + 6c = $90
multiply by -5
-20a - 35c = -$415
20a + 24c = $360
-11c= -$55
c = $5 child tickets
4a + 7(5)= $83
4a + 35 = $83
4a = $48
a= $12 adult tickets