The equilibrium price is $80 and the equilibrium quantity is 28 million tablets. The part of the demand curve above the equilibrium and to the left shows buyers who would have paid more: at point J, for example, 20 million tablets would sell at $90. Those buyers paid $80 and received a benefit beyond what they paid. The amount people would have been willing to pay minus what they actually paid is consumer surplus, the area F above the market price and below the demand curve.
The supply curve shows what firms would accept. At point K, firms would still supply 14 million tablets at $45; those firms received $80 instead. The price received minus the price a producer would have accepted is producer surplus, the area G between the market price and the supply curve below the equilibrium.
Consumer surplus plus producer surplus is social surplus, F + G. It is larger at the equilibrium quantity than at any other quantity, which is the sense in which the market equilibrium is efficient. Turn on the shading to see the two areas, and shift a curve to see how they change.