[tex]\frac{a}{b} = \frac{3}{5} \ \ \rightarrow \ \ \frac{b}{a} = \frac{5}{3}\\\\\frac{4a-3b}{a} = \frac{4a}{a} - \frac{3b}{a} = 4 - 3\cdot\frac{5}{3} = 4-5 = -1[/tex]
