Answer: x = 20.
Step-by-step explanation:
x and (3x + 10) combine to form a right angle, shown in the diagram by the small square joining the perpendicular lines.
Right angles are 90 degrees, so you can add both angles to get 90:
[tex]x + (3x + 10) = 90\\\\4x + 10 = 90\\\\4x = 80\\\\x = 20[/tex]
