How do you divide 5 into 8.4?

Long division.

Start by dividing 5 into 8.

8/5 = 1 r3

Put a decimal place after the 1.

1.

Now take the remainder and append the decimal to the right of it:

34

Divide 5 into 34

34/5 = 6 r4.

Append to the right of the decimal.

1.6

Repeat using 0s as placeholders after the 8.4 has been exhausted, and repeat until you get a remainder of 0, or a sufficient number of significant digits:

40/5 = 8 r0

1.68

Remainder is 0, so 5 divides into 8.4 exactly 1.68 times.

To test this, multiply 5 by the answer:

5 * 1.68 = 8.4