It is more convinient to use substitution
For the first problem, a "fifth" means divided by 5, so "four-fifths of b" means

or

Subtract means to take away, so "6 subtracted from" means to "take away 6" or -6
As such, the answer to the problem would be

The rest the problems are also just translating English to math.
4u^2 + 4u + 3 - 2u^2 = 2u^2 + 4u + 3 <==
F(x) = x^2 - 2x - 95
solving by completing the square: f(x) = ( x - 1 ) ^2 - 96,
0=6x^3+8
-8 -8
-8=6x^3
---- ------
6 6
(-8)/6=x^3
cube root each side to get
∛[(-8)/6]=x or F(x)=∛[(-8)/6]
F(x)=-1.100642...