Write it down.
Easy and simple
c.
The number of students is represented with S, to show 2 times that number it is shown as 2S, a less than is word problem jargon for minus. So it is 2S-21.
To factor a quadratic of the form ax^2+bx+c you need to find two values, j and k, which satisfy two conditions...
jk=ac=12 and j+k=b=8, so j and k must be 2 and 6
Then the factors are just (a+j)(a+k), in this case:
(a+2)(a+6)
So the missing term was 6
When converted to a household measurement, 9 kilograms is approximately equal to a
So firstly, you want to foil - (7v^4 + 6) [Think of the minus sign as -1]: 
Next, combine like terms and your answer will be: 