For the circuit shown above what value of inductance L yield

For the circuit shown above, what value of inductance L yields a value of LT equal to 7.5 nH?

a. 24 nH

b. 5 nH

c. 10 nH

d. 20 nH

LT=L+(5n*L)/(5n+L)

7.5n=L+(5n*L)/(5n+L)

7.5n=(5nL+L^2+5nL)/(5n+L)

37.5n^2+7.5nL=5nL+L^2+5nL

L^2+2.5*10^-9L-37.5*10^-18=0

L=5*10^-9 H

L=5 nH.