Help please.

Step-by-step explanation:

so the probably seems impossible b/c there is some "implied" knowledge. You are supposed to remember that interior angles of a triangle add up to 180 °.   Which I bet you knew.. .huh

so let's put that knowledge to work to help us solve this

we can say that all of the angles add up to 180 like this:

180 = (x-4) + (11x-11) + (x+13)

see? now group all the like terms, that is, put the x'es together & the numbers

180 = 13x -2

see?  I just grouped the x terms and the constant terms, now move the 2 arcoss the equal sign to the other side, by adding 2 to both sides

182 = 13x

see?  now divide both sides by 3  :)

14 = x  

now we know what x is so plug that into the expression for the C angle

∠C = x-4

∠C = 14-4

∠C = 10 °

there you go.   :)

best of luck, just leave a message in the comments if you have more questions  , I'll see it there  :)

it is contrapositive

i could not see the question too well so check yourself again too . this is because i want you to get it correct.