Give each month a number:
January = 0
February = 1
March = 2
April = 3
Now set X to 3 in the equation ad solve for t.
t = -30cos(x/6) +60
t = -30cos(3/6) +60
t = 33.672 degrees. ( Round as necessary)
You would need to change the +60 to a new starting point based on what the rise in temperature is due to global warming.
