Analysis: This question examines the application of one-dimensional linear equation. From the meaning of the question, we can know that comic books are three times as many as story books after x days. According to comic books, list the equations and solve them.

The problem solving process is as follows:

Solution: Suppose the comic book after X days is three times as big as the story book. According to the meaning of the title,

140-4x=3×( 100-4x)

140-4x=300- 12x

The transferred project is 12x-4x=300- 140.

8x= 160

x=20

A: There are three times as many comic books as story books left in 20 days.

Extended data:

One-dimensional linear equation refers to an equation with only one unknown number, the highest order of which is 1, and both sides are algebraic expressions. A linear equation with one variable has only one root.

Root seeking method

conventional process

There are five steps to solve a linear equation with one variable, namely, denominating, removing brackets, shifting terms, merging similar terms, and the transformation coefficient is 1. All steps are carried out according to the properties of algebraic expressions and equations.

In one-dimensional linear equations, the denominator removal step is usually multiplied by the least common multiple of each denominator. If the denominator is a fraction, it can be replaced by the other part of the item multiplied by the reciprocal of the fraction on the denominator. ?

If there is an irrational number on the denominator, it is necessary to make the denominator rational first.