Let X be any thermometric property that varies linearly with temperature. X can be the
length of a metal rod, the height of a column of mercury, the electrical resistance of a wire,
the pressure of a gas, etc.
X ∝ T
Since X has linear variation with T, a plot of X versus T is a straight line:
X = C · T + X0
X0 is the value of X at T=0. In the Celsius scale
And C is the slope = (1.60- . 75 )/ (105 - 90)
= .85 / 15
to find out X0 = X - CT
= 1.60 - (.85/ 15 ) x 105
= A suction of 4.95 atm