Out of 53 teachers 36 drink tea 18 drink coffee, 10 drink neither. how many drink both?

Out of 53 teachers 36 drink tea 18 drink coffee, 10 drink neither. how many drink both?

Let T be tea drinkers
Let C be coffee drinkers
Let (T & C) be Tea & Coffee drinkers.
And 53 are total. So we use the Union formula relation:

C U T = C + T - (C & T)
53 = 18 + 36 - (C & T)

C & T = 53 - (Not C & Not T) since we subtract people who don't drink coffee and don't drink tea
C & T = 53 - 10 = 43
C U T = 18 + 36 - 43
C U T = 11