So you subtract $22.89 from $54.73 to get a total of $31.84 and that’s how much the customer paid.
By the law of cosines, the angle

satisfies

which reduces to

which converts to approximately 77 degrees (this can be done my multiplying by 180 and dividing by pi).
If Jeff writes comic strips at a rate of 3 comics an hour then you must put 3,4,7&9 into the function and add up the products.
9+12+21+27=69