Someone please explain This is the third time i post this question

Use Cramer's rule to find the solution to the following system of linear equations.
x-2y = -7
5x-9y=-5

Arefrigeration system at your company uses temperature sensors fixed to read celsius (°c) values, but the system operators in your control room understand only the fahrenheit scale. you have been asked to make a fahrenheit (°f) label for the high temperature alarm, which is set to ring whenever the system temperature rises above –10°c. what fahrenheit value should you write on the label?