Answer:
54 degree was Monday high temperature
Explanation:
As per the given statement:
Wednesday high temperature =

It is also given that Tuesdays high temperature was 12 degrees cooler than Mondays and 7 degrees cooler than Wednesdays.
Tuesday temperature = 12 degree + Monday Temperature
and
Tuesday temperature = 7 degree + Wednesday temperature.
Then, by substituting the given values;
⇒Tuesday temperature = 7 degree + 59 degree = 66 degree.
To find the Monday high temperature.
Monday high temperature = Tuesday temperature - 12 degree
= 66 - 12= 54 degree.
Therefore, 54 degree was Monday high temperature