$$\textbf{Step -1: Convert all the given decimals into like decimals.}$$
$$\text{Among }).007,8.5\text{ and }30.08,$$
$$0.007\text{ has maximum decimal places, i.e. }3.$$
$$\text{Write }8.5\text{ and }30.08\text{ also to three decimal places.}$$
$$\therefore 8.5=8.500$$
$$\text{and }30.08=30.080$$
$$\textbf{Step -2: Add them.}$$
$$\text{Now, simply add the three decimal numbers from right to left }$$
$$\text{and place a decimal point after three places from right.}$$
$$0.007+8.500+30.080=38.587$$
$$\textbf{Hence, 0.007+8.5+30.08=38.587}$$