Ok, so
We want to find the side b.
For this, we can use the trigonometric functions, as this:
We know that tan(x) relations the opposite side of the angle and its adjacent side. So, we replace:
tan(x) = opposite side / adjacent side
Now,
tan(40°) = b / 6.
We can find b multiplying tan(40°) * 6
Remember that tan(40°) is a number, and this is 0,839 approximately.
So, b is equal to 0,839*6, and this is 5.03
Rounded to the nearest tenth: The answer is 5.0