The month of January has 31 days, so from January 1st to February 14th, there are 31 + 14 or 45 days, namely x = 45.
y = 3.06 * sin[ 0.017(45) - 1.40 ] + 12.23.
make sure your calculator is in Degree mode.
First you need to simplify the left side of the equation to get

Then you add by two on both sides to get

Finally you divide by 2 on both sides to get
131.3312, and if rounded 131
X/5-4
The quotient of a number x and 5 is x/5.
Four less means you will subtract 4 from it.