David H. answered • 02/03/17

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This is a separable differential equation.

dT/dt = k(T-80)

move dt to fight and divide by T-80

dT/(T-80) = kdt

integrate

ln|T-80| = kt + C

you are given temp is 190 at t= 0.7. And temp at t = 0 is 290.

so t = 0

ln(210) = C

t = 0.7

ln(110) = 0.7k+ln210

so k = ln(110/210)/0.7

now plug in t = 3.

hope helpful

Beat - david