Chapter 1 - Solving Linear Equations - 1.1 - Solving Simple Equations - Exercises - Page 9: 35

$a=5.6$

Use the Addition Property of Equality by adding $0.4$ to both sides of the equation: $$\begin{align*} 5.2+0.4&=a-0.4+0.4\\ 5.6&=a\end{align*}$$ Check the solution by substituting $5.6$ to the variable in the given equation: $$\begin{align*} 5.2&=a-0.4\\ 5.2&\stackrel{?}{=}5.6-0.4\\ 5.2&\stackrel{\checkmark}{=}5.2\end{align*}$$ Thus, the solution is $a=5.6$.