On a temperature scale ' X ', the boiling point of water is 65 ° X...

The relation between two temperature scales can be written as follows

$\dfrac{65 - x}{65 - \left(- 15\right)} = \dfrac{212 - F}{180} . . . \left(1\right)$

Substitute the values of the known parameters in to equation (1) and sole to calculate the required temperature in Fahrenheit scale.

$\begin{cases}\dfrac{65 + 95}{80} & = & \dfrac{212 - F}{180} \\ & ⇒ & 2 \times 180 = 212 - F \\ & ⇒ & F = 212 - 360 \\ & = & - 148 ° F\end{cases}$