Step I: Calculation of VTh

Removing the $30 \ \Omega $ resistor from the network. 

Mesh 1 and Mesh 2 from a supermesh. 

Writing current equation for supermesh. 

$I_1-I_2=13\ \ \ ..........................(1)$

Writing voltage equation for supermesh

$150-15I_1-60I_2-40I_2=0\\ 15I_1+100I_2=150\ .....................(2)$

Solving equations (1) and (2) 

$I_1=-10\ A, \ \ \ I_2=3A$

Writing VTh equation

$40I_2-V_{Th}-50=0\\ V_{Th}=40I_2-50\\ V_{Th}=40(3)-50=70\ V$

Step II:*Calculation of RTh*: 

Replacing the voltage sources by short circuits and the current source by an open circuit, 

$R_{Th}=75\ ||\ 40=26.09\ \Omega $

Step III: Calculation of IL:

$I_L=\dfrac{70}{26.09+30}=1.25\ A$