3. Check whether 7 + 3x is a factor of \(3x^3 + 7x\).

Let \(p(x) = 3x^3 + 7x\)

To check, whether 7 + 3x is a factor of \(3x^3 + 7x\).By factor theorem, \(7 + 3x = 0\) i.e. x = -7/3

So, \(p(-7/3) = 3(-7/3)^3 + 7(-7/3)\)

i.e. \(p(-7/3) = - 3×(343/27) - 49/3\)

i.e.\(p(-7/3) = -1470/27\)

i.e.\(p(-7/3) = -490/9\)

Hence, 7 + 3x is not the factor of \(3x^3 + 7x\) since the remainder is not zero.