Evaluate the integral.
14∫ x³ √ x² + 8 dx

a.14/3 (x² + 8) ³/2 - 112(x² + 8)¹/² + c
b.14/5 (x²+8) 5/2+112/3(x²+8) 3/2 + c
c.14/5 (x²+8) 5/2 - 112/3(x²+8) 3/2 + c
d. 14/3 (x² + 8) ³/2 - 112(x² + 8)¹/² + c