Since the denominators of the two fractions are different, we need to make them same and then add the two fractions
[tex] \frac{5}{ m^{2}  n^{2} } + \frac{m}{n}  \\  \\ 
[/tex]
LCM is m²n² . So we can write:
[tex] \frac{5}{ m^{2}  n^{2} } + \frac{m}{n}  \\  \\ 
= \frac{5}{ m^{2}  n^{2} }+ \frac{m(m^{2}n) }{ n(m^{2}  n) } \\  \\ 
= \frac{5}{ m^{2}  n^{2} }+\frac{m^{3}n }{ m^{2}  n^{2} } \\  \\ 
= \frac{5+m^{3}n}{m^{2}  n^{2} } [/tex]