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

It is clear from the graph that lowest point for scale A is 30° and lowest point for scale B is 0°. Highest point for the
scale A is 180° and for scale B is 100°. Hence, correct relation is

                         $\frac{t_A-(\mathrm{LFP}{)}_A}{(\mathrm{UFP}{)}_A-(\mathrm{LFP}{)}_A}=\frac{t_B-(\mathrm{LFP}{)}_B}{(\mathrm{UFP}{)}_B-(\mathrm{LFP}{)}_B}$

where, LFP = lower fixed point
and UFP = upper fixed point.

$\Rightarrow$           $\frac{t_A-30}{180-30}=\frac{t_B-0}{100-0}\Rightarrow \frac{t_A-30}{150}=\frac{t_B}{100}$