Question 947676
Many people may not know what the variables mean.


Most of the way down in the article:
http://en.wikipedia.org/wiki/Convective_heat_transfer#Newton.27s_law_of_cooling


Refering to the equation you presented,
U, temperature after time t
T, temperature of the environment
Uo, temperature initially
t, amount of time passage.
The exponent should be {{{kt}}}.


The data in problem description:
{{{highlight_green(42=75+(35-75)e^(k*5))}}};
Check to see that each given value is in the correct place for its meaning.  This equation will allow you to solve for k.  


Once k is found, you have a model more like:
{{{U=75+(35-75)e^(k*8)}}}
but now you would have found k and can evaluate U.