Pablo needs 90 paper plates for a birthday party. He already has 39 blue plates and 15 red plates. How many more plates should Pablo buy?

$${\mathtt{39}}{\mathtt{\,\small\textbf+\,}}{\mathtt{15}} = {\mathtt{54}}$$ 

$${\mathtt{90}}{\mathtt{\,-\,}}{\mathtt{54}} = {\mathtt{36}}$$

Pablo needs 36 more paper plates to make 90

 

Unless it's a trick question where blue and red plates arn't paper in which case he needs 90 paper plates