Chapter 3 - Equations and Problem Solving - 3.1 - Solving First-Degree Equations - Problem Set 3.1 - Page 100: 72

$x=-12$

We start with the given equation: $-4.2x=50.4$. We divide by $-4.2$ on both sides of the equation in order to get $x$ by itself: $\frac{-4.2x}{-4.2}=\frac{50.4}{-4.2}$ We simplify the fractions by dividing: $x=-12$