After 10 innings a batter has a certain average. In the 11th innings he scores 96 runs, and this lifts his average by 4 runs. What is his average after the 11th innings?

Let the average after 10 innings be $x$. Then $10x+96=11(x+4)$, so $10x+96=11x+44$ and $x=52$, making the new average 52 + 4 = 56 runs. Read it the quick way: the 96 has to reach the new average of $x+4$ and also lift each of the 10 earlier innings by 4, so $96=(x+4)+40$. 52 is the average BEFORE the 11th innings, one step short. 60 adds the 4-run rise a second time to an answer that already includes it. 96 is the score in that innings, which stands 40 runs above the new average.