The Fahrenheit temperature scale still used in English-speaking countries is defined as follows

The Fahrenheit temperature scale still used in English-speaking countries is defined as follows: 0C and 100C are 32F and 212F; the interval from 32F to 212F is split into 180 equal parts. What is the reading of a Fahrenheit thermometer when it is immersed in 50C water?

50 degrees Celsius corresponds to half the scale from 0 to 100 degrees Celsius, that is:

since the interval from 32 degrees Fahrenheit to 212 degrees Fahrenheit is divided into 180 equal parts, that is, one part is (212 – 32) / 180 = 180/180 = 1 degree Fahrenheit.

Half of the scale will be 180/2 = 90 equal parts.

That is, 50 degrees Celsius is 32 + 1 * 90 = 32 + 90 = 122 degrees Fahrenheit.