It is an isosceles triangle, therefore
[tex]m\angle A=m\angle B[/tex]
[tex]4x+5=5x-1\ \ \ |-5\\4x=5x-6\ \ \ |-5x\\-x=-6\to x=6[/tex]
[tex]m\angle A=m\angle B=4\cdot6+5=24+5=29^o[/tex]
We know:
[tex]m\angle A+m\angle B+m\angle C=180^o[/tex]
therefore
[tex]29^o+29^o+m\angle C=180^o\\\\58^o+m\angle C=180^o\ \ \ |-58^o\\\\m\angle C=122^o[/tex]
