You have to know how the value of one unit corresponds to the value of the other unit. For example you have to know that there are 100 cm in 1 m or 1000 m in 1 km. It's easy in metric measurement system because it's all about multiplying/dividing by 10 or its multiplications. But in American/English system you just have to learn the values.
For example:
1 km = 1000 m = 10000 dm = 100000 cm = 1000000 mm
But:
1 mile = 1760 yards = 5280 feet = 63360 inches
<span>x : y is equal to 12 : 8. These can be reduced or cancelled down to 3 : 2 in the same proportions. Therefore, when y is 12, you have to multiply the smallest value y can be by 6, and must do the same to the smallest x value to retain the proportions. x = 18 when y = 12.</span>
P% = p/100
20% = 20/100 = 2/10 = 0.2
20% of 70 plants:
"0.2 x 70 plants = 14 plants"

SQRT each individual bit: 4 and

and 9 and