Input impedance of lossless transmission line
I'll try to help. Firstly, consider this: the line on the right side has a load of Zl and a length 3(Wavelength)/4. So you get the value of  tan(βl1)=tan(3π2)→∞,  Now, consider the formula given. Taking out  tan(βl) term as common from both the numerator and denominator, you get the equation as 

$$Z_{(l)}= Z_o{(Z_lcot(bl)+jZ_o)/(Z_ocot(bl)+jZ_l)}$$

Now note that as tan goes to infinity, cot goes to zero...
Hence, Z(l) results in (Zo)^2/Zl.
Hence , you can now find Z(l). Further, this Z(l) acts as the load for the second transmission line(l2). Similarly, you get the required answer.