The answer is[tex]\frac{a-b+2}{abc^{3} }[/tex]
The expression is [tex] \frac{a-1}{abc^{3} } + \frac{3-b}{abc^{3} } [/tex]
Since [tex] \frac{a}{x} + \frac{b}{x} = \frac{a+b}{x} [/tex], then:
[tex] \frac{a-1}{abc^{3} } + \frac{3-b}{abc^{3} } = \frac{a-1+3-b}{abc^{3} }= \frac{a-b-1+3}{abc^{3} }=\frac{a-b+2}{abc^{3} }[/tex]
