<span>The object's speed is 8/5 miles per hour or 1.6 mph.</span>
All the interior angles of a triangle always add up to 180 degrees.
3x + (2x + 20) + (4x - 20) = 180
3x + 2x + 20 + 4x - 20 = 180
3x + 2x + 4x + 20 - 20 = 180
10x = 180
x = 180/10
Therefore, x = 18