The correct option is C 2x3+x2−3x+14
Let the expression to be added be Y.
(x3+3x−8)+Y=(3x3+x2+6)
To get 3x3,we need to add 2x3 as first term to x3in (x3+3x−8)
Similarly, as we don't have x2 in (x3+3x−8).We need to add x2as second term
Similarly, we have an extra 3x in (x3+3x−8).So, we need to add -3x.as third term
Similarly, to make -8 to +6 we need add 6 + 8 = 14 to (x3+3x−8).So, we need to add 14 as fourth term
So we have to add (2x3+x2−3x+14) to (x3+3x−8), to get the expression (3x3+x2+6).