Evaluate the integral: ${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{\sqrt[\phantom{2}]{4x^2-49}}{x^3}dx$

a$.$ Which trig substitution is correct for this integral?

A$.x=\frac{7}{2}sec()$

B$.x=\frac{7}{2}sin()$

C$.x=\frac{49}{4}sec()$

D$.x=\frac{2}{7}sec()$

E$.x=\frac{1}{4}sec()$

b$.$ Which integral do you obtain after substituting for $x?$

c$.$ What is the value of the above integral in terms of $?$

d$.$ What is the value of the original integral in terms of $x?$