What is 1/4 of 10 explain

Too many points for such a simple explanation :)) Whatever:
To get 1/4 of a number you multiply the number by 1/4. Same for any non-percent number. If the number is a percent, say, 23,5%, you first divide it by 100 to get a non-percent, then do the same, that is, multiply it by the number.
Our result is

A= r2 × 3.14 7x7 ↓ ↓ 49 × 3.14 = 153.86 → 153.9

M< 5 = 80 , < 2 = 80, < 6= 100, < 3= 100, < 7= 80, < 4= 80, < 8= 100