For this case what we must do is use the law of cosines.
We then have the following equation:

Where,
a, b: sides of the triangle
x: angle between sides a and b.
Substituting values we have:

Clearing the value of c we have:
Answer:
An expression that is equivalent to how many feet the oak trees are from each other is:
Step-by-step explanation:
a.120÷100×20
profit=24
=24+120
=144
b.289÷100×15
=43.35
289-43.35
=245.65
sqrt (-1) = i the imaginary number
so the negative sqrt (-1) = -i