Answer:
(a)His monthly Interest Rate=0.8%
(b)Annual Interest Rate = 9.6%
(c)
Step-by-step explanation:
For a Principal P invested at a yearly rate r, compounded m times in t years
Amount at Compound Interest= 
Comparing with Jerry's equation y=388 (1.008)
(a)His monthly Interest Rate= 0.008=0.8%
(b)Annual Interest Rate= Monthly Interest Rate X 12 =0.8 X 12 = 9.6%
(c)If I invest $500 at the same rate of return,
Total Money after m months
= 


The slope will be -1/2. If you put it into slope intercept form of y=mx+b, mx will always be the slope.
You can't. If you think about the straight line on a graph, those numbers
describe a single point that the line goes through, and they don't tell you
anything about the slope of the line, or where it crosses the x-axis or the
y-axis. So I don't think you can tell the constant of variation from one point.