Try to get into the habit of checking your answers. For this example, substituting t(x?) = 5 and t = 17 should get you temperatures of 40 and 80 respectively.
It doesn't work does it ?
Think again about the period, (it isn't 12), and also the phase shift, (it isn't zero).
Ask yourself at what times you want your first term to be zero, giving you a temperature of 60.