For the given triangle, DE = 6.97 units.
Explanation:
Step 1:
In the given triangle, the angle is 55°. The adjacent side has a length of 4 units and assume the hypotenuse, DE measures x units.
To calculate the value of x, we determine the cos of the triangle where we divide the length of the adjacent side by the length of the hypotenuse.

Step 2:
The length of the adjacent side = 4 units.
The length of the hypotenuse = x units.
The angle of the triangle = 55°.

So x = DE = 6.9747 units, rounding this off to the nearest hundredth we get DE = 6.97 units.