The graph between two temperature scales P and Q is shown in the figure. Between upper fixed point and lower fixed point there are 150 equal divisions of scale P and 100 divisions on scale Q. The relationship for conversion between the two scales is given by: 

A

$$\frac{t_Q}{150} = \frac{t_P - 180}{100}$$

B

$$\frac{t_Q}{100} = \frac{t_P - 30}{150}$$

C

$$\frac{t_P}{180} = \frac{t_Q - 40}{100}$$

D

$$\frac{t_Q}{100} = \frac{t_P - 180}{150}$$