Mathematical Format Selection: Identifying Correct Notation Forms

To correctly set up a vertical addition of decimal fractions, it is crucial to align the numbers by their decimal points. Let's break down the choices:

• Choice 1 presents the numbers in the proper format. The decimal points of $15.5604$ and $4.32$ align vertically, ensuring accurate addition.

• Choice 2 misaligns the decimal points, incorrectly starting $4.32$ further to the left than necessary.

• Choice 3 also misaligns the decimals, wanting to begin $4.32$ even further than choice 2.

Thus, the correct choice is Choice 1, since it correctly aligns the numbers by their decimal points, facilitating accurate addition of the values involved.

Therefore, the correct format choice is Choice 1.