the low temp in chicago is 25 degrees, occurs in january. x = 1(january)

average high is 75 degrees which occurs in july. x=7(july)

determine the constants so that the function models the data, where f(x) gives the temperature as a function of x.

this is what I have:

it just doesn't look right to me. though, when i go to 2nd => calc => value, it gives me close to the exact values being off only by a hundred or less.