The equation of a vertical line has what format

You are on a cycling trip around europe with friends. you check the weather forecast for the first week. these are the temperatures for the week. sun mon tues wed thurs fri sat 16°c 20°c 24°c 28°c 28°c 23°c 15°c what is the mean temperature forecast for the week?

The anwser cause i do not understand just plez

In the diagram below, abc is congruent to dec what is the value of x