1200x+4=800x，
Solution: x=8,
It is verified that x=8 is the solution of the original equation. When x=8, x+4= 12.
A: Last year, the unit price of literature books was 8 yuan, and that of popular science books was 12 yuan.
(2) Suppose this school bought Y literary books this year.
8×( 1+25%)y+ 12(200-y)≤2 135，
y≥ 132 12，
∫y is an integer,
The minimum value of y is133;
A: This middle school should buy at least 133 literature books this year.