If the point $(3, 5)$ lies on the graph of the equation $ax + y = 20$,find the value of $a$.

The linear equation $2x - 5y = 7$ has:

Draw the graphs of linear equations $y=x$ and $y=-x$ on the same Cartesian plane.
What do you observe?

Determine the point on the graph of the linear equation $2x + 5y = 19$,whose ordinate is $1 \frac{1}{2}$ times its abscissa.

Draw the graph of the equation represented by a straight line which is parallel to the $x$-axis and at a distance $3$ units below it.

The linear equation that converts Fahrenheit $(F)$ to Celsius $(C)$ is given by the relation:
$C = \frac{5F - 160}{9}$
$(i)$ If the temperature is $86^{\circ} F$,what is the temperature in Celsius?
$(ii)$ If the temperature is $35^{\circ} C$,what is the temperature in Fahrenheit?
$(iii)$ If the temperature is $0^{\circ} C$,what is the temperature in Fahrenheit? And if the temperature is $0^{\circ} F$,what is the temperature in Celsius?
$(iv)$ What is the numerical value of the temperature which is the same in both the scales?