# Chapter 7 - Section 7.1 - Systems of Linear Equations in Two Variables - Concept and Vocabulary Check - Page 817: 4

$-2$.

#### Work Step by Step

When using the addition method, we need to have the opposite value of the coefficients before the variable. Thus, we need to multiply the second equation by a factor of $-2$, so that the coefficient of $y$ becomes $-10$ such that the variable $y$ will be cancelled when adding the two equations. In other words, the answer is $-2$.

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