155-5x= 15，x=28

Supplementary information: A linear equation of one variable 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. One-dimensional linear equation can solve most engineering problems, travel problems, distribution problems, profit and loss problem, integral table problems, telephone billing problems and digital problems.

One-dimensional linear equations were first seen in ancient Egypt about BC 1600]. Around 820 AD, the mathematician Hua La Zi Mi put forward the idea of "merging items" and "shifting items" in his book "Eliminating Yuan and Reducing Yuan". In16th century, after the mathematician David founded symbolic algebra, he put forward the propositions of shifting terms and division of the same equation. 1859, mathematician Li officially translated this kind of equations into linear equations.