Actually Welcome to the Concept of the Triangles.
Since we know that, the Angle sum property of a triangle is equal to 180°.
means that, <A + <B + <C = 180°
so we can write as,
==> 2x-10 + x + 30 +70 = 180°
===>3x +90 = 180
==> 3x = 90
hence, x = 30°
so now, substitute angle x,
So angle A is => 2(30)-10 => 60-10 = 50°
hence Angle A = 50°.