Hector serves ice cream at a local ice cream shop. he sells 19 ice cream cones on sunday,27 ice cream cones on sunday, and 153ice cream cones for the entire week. how many ice cream cones did hector sell on the weekday?

So, what you want to do here is subtract the ice cream sold on the weekend from the ice cream that was sold during the rest of the week.
He sold 19 on Saturday and 27 on Sunday, so these numbers need to be subracted from your total for the week.

(Total Sold) - [(Amount sold Saturday) + (Amount sold Sunday)] = (Amount sold on weekdays)

153 - (19 + 27) = X
153 - 46 = X
107 = X