If 105 customers were the total, and 35% prefers cake, we must calculate 35% of 105, then we must do 105 multiplied by 35%, we can doit transforming the 35% in the fraction notation:

And the multiplication

Therefore, if we round it to the nearest whole number, the number of customers that prefer cake is 37.
37 customers prefer cake.
$4680
Since 18% is 18/100 you just have to multiply the $842.4 by the reciprocal of that to find your answer
Reciprocal of 18/100 is 100/18
842.4* 100/18 equals 84240/18
84240/18 equals 4680