Z=9 because when you replace the z with the 9 the problem would be then 5(9)+2. You multiply the 5 and 9 which then would equal 45 and then add 2 which would end up being 47. This is correct because the triangle is isosceles and isosceles is a triangle with 2 angles that are the same and 1 that isn't so they have to be the same. Hope this makes sense :)
