The sum of all 3 angles is 180 degrees, you should be able to solve from here.
x = 
isolate 5x by adding c to both sides of the equation
5x = k + c ( divide both sides by 5 )
x = 
Answer:
is this supposed to say 7.7 x
? if so then it's 770 (you move the decimal over 2 places to the right)