story problem trouble

Question

For this story problem, I could solve part a, but not part b. Help please? Thanks!

 

 

In 1870 the average ground temperature in Paris was 11.8°C. Since then it has risen at a nearly constant rate, reaching 13.5°C in 1969.

(a) Express the temperature T (in °C) in terms of time t (in years), where t = 0 corresponds to the year 1870 and 0 ≤ t ≤ 99. (Give your answer in slope-intercept form.)

T=17t/990   +11.8


(b) During what year was the average ground temperature 12.4°C? (Round your answer down to the nearest year.)

????

Answer 1

T=17t/990 +11.8 is assumed to be correct.

(b) During what year was the average ground temperature 12.4°C? (Round your answer down to the nearest year.)

 

T=12.4; substitute into above formula & solve for t.  Add 1870 to t to get the full year number when this temperature T was attained.