The width of a rectangle is 3.4 units and the length is twice the width. the perimeter of this rectangle is how many units?

First, you must make sure that since the length is twice as big as the length.  That means that the length would be 6.8 because 3.4 x 3.4 = 6.8.  Then, since a rectangle has two long sides and two short sides, you add 6.8 + 6.8 + 3.4 + 3.4,  which equals 20.4(perimeter).

  b.  98.5°

Step-by-step explanation:

There are a number of ways to do this. Perhaps one of the simplest is to compute the angle associated with each vector, and find the difference.

We can compute that angle as ...

  vector angle = arctan((coefficient of j)/(coefficient of i))

where the arctangent is computed in the appropriate quadrant according to the signs of i and j.

  ∠u = arctan(-8/√5) ≈ -74.38°

  ∠v = arctan(1/√5) ≈ 24.09°

The angle between these vectors is then ...

  24.09° -(-74.38°) = 98.47° ≈ 98.5°