The graph between two temperature scales A and B is shown in the figure. Between upper fixed and lower fixed points, there are 150 equal divisions on scale A and 100 on scale B. The relationship for conversion between the two scales is given by 

                                     

1. tA-180100=tB150

2. tA-30150=tB100


3. tB-180150=tA100


4. tB-40100=tA180