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
84 divide by 112 = 0.75
21
84
84 42,2 21,2,2 7,3,2,2
Start by subtracting 32 from 84. Then multiply the answer by 5 and divide by 9. In this case the answer is 28.8 degree celsius.
6/84 = 0.071428571
3
Divide each part by 42, to give 2 over 5.
543.7857
4.9048
40
Both 84 and 120 are products of 12. If you divide 84 by 12, you get 7 and if you divide 120 by 12 you get 10. Therefore 84/120 = 7/10.