The epa says the value of a human life is $7.6 million, measured from birth to death. if life expectancy is 78 years, what is the value of the remaining life of a 52-year old person?

The value would be $2.53 million.

Set up a proportion to solve this:

7.6/78 = x/(78-52)

[7.6 million for 78 years; x million for 78-52 years remaining]

Cross multiply:
7.6(78-52) = x*78
7.6(26) = 78x
197.6 = 78x

Divide both sides by 78:
197.6/78 = 78x/78
2.53 = x

The interest rate would be 2.4%.

We start out finding the total amount he pays, including interest. 

78.40/month * 12 months * 5 years = $4704

We take off the amount of principal:
4704-4200 = 504

This is the amount of interest he pays.  Now we use the simple interest formula, I=prt:

504=4200(r)(5)

Multiply 4200 and 5:
504=21000r

Divide both sides by 21000:
504/21000 = 21000r/21000
0.024 = r
2.4% = r