Area = 1/2 * base * height
= 1/2 * 20 * 6
= 1/2 * 120
= 60 ft^2
Sure but wheres the picture?
Given equation is y=2x+7 and 
Let's simplify the 2nd equation
before we can start graph so that calculation will be easy

multiply both sides by 2 to cancel out fractions

y=2x+7
which is exactly same as the first equatoin so graph of both will be exactly same and solution will be infinitely many solutions.
y=2x+7 has y-intercept 7 so first point will be (0,7). Slope is 2 so rise 2 unit up then 1 right and graph the new point.
Answer:α
=
71
°
:
explain:
From trigonometry we have:
cos
α
=
7
21
7
=
21
cos
(
α
)
and:
α
=
a
r
c
cos
(
7
21
)
=
70.5
≈
71
∘