Convert to percentage:

$$
\frac{19}{100} \times 100\%
$$

$$
\boxed{19\%}
$$

$$
\frac{3}{5} \times 100\%
$$

$$
3 \times 20\% = \boxed{60\%}
$$

$$
\frac{7}{10} \times 100\%
$$

$$
7 \times 10\% = \boxed{70\%}
$$

$$
0.21 \times 100\%
$$

$$
\boxed{21\%}
$$

$$
0.05 \times 100\%
$$

$$
\boxed{5\%}
$$

$$
0.8 \times 100\%
$$

$$
\boxed{80\%}
$$

$$
3.76 \times 100\%
$$

$$
\boxed{376\%}
$$

$$
2\frac{3}{5} = \frac{2 \times 5 + 3}{5} = \frac{13}{5}
$$

$$
\frac{13}{5} \times 100\%
$$

$$
13 \times 20\% = \boxed{260\%}
$$

$$
2.5 \times 100\%
$$

$$
\boxed{250\%}
$$

$$
\frac{10}{100} \times 60
$$

$$
\frac{1}{10} \times 60 = \boxed{6}
$$

$$
\frac{20}{100} \times 45
$$

$$
\frac{1}{5} \times 45 = \boxed{9}
$$

$$
\frac{40}{100} \times 160
$$

$$
\frac{4}{10} \times 160 = 4 \times 16 = \boxed{64}
$$

$$
\frac{30}{100} \times 120
$$

$$
\frac{3}{10} \times 120 = 3 \times 12 = \boxed{36}
$$

$$
\frac{22}{100} \times 1000
$$

$$
22 \times 10 = \boxed{220}
$$

$$
\frac{35}{100} \times 240
$$

$$
\frac{35}{10} \times 24 = \frac{7}{2} \times 24 = 7 \times 12 = \boxed{84}
$$

$$
\frac{5}{100} \times 800
$$

$$
5 \times 8 = \boxed{40}
$$

$$
\frac{18}{100} \times 3600
$$

$$
18 \times 36 = \boxed{648}
$$