The two marks on the angles A and C suggest that those angle are the same, and thus the triangle is isosceles.
So, if the measure of angle C is x, the measure of angle A will be x as well.
To solve the exercise, we must use the fact that the sum of the interior angles of any triange is always 180°.
In our case, the measures of the angles are 70, x and x, so the equation is
