Least common multiple of $4$ and $5$ is $20$. Convert $\frac{5}{4}$ and $\frac{1}{5}$ to fractions with denominator $20$.
$$\frac{25}{20}+\frac{5}{c}-\frac{4}{20}$$
Since $\frac{25}{20}$ and $\frac{4}{20}$ have the same denominator, subtract them by subtracting their numerators.
$$\frac{25-4}{20}+\frac{5}{c}$$
Subtract $4$ from $25$ to get $21$.
$$\frac{21}{20}+\frac{5}{c}$$
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $20$ and $c$ is $20c$. Multiply $\frac{21}{20}$ times $\frac{c}{c}$. Multiply $\frac{5}{c}$ times $\frac{20}{20}$.
$$\frac{21c}{20c}+\frac{5\times 20}{20c}$$
Since $\frac{21c}{20c}$ and $\frac{5\times 20}{20c}$ have the same denominator, add them by adding their numerators.
