Sine and cosine (and trigonometric functions in general) are used extensively in physics, and neither really has priority - it depends on the particular problem you're working on. Is there a particular problem that prompted your question?
7) a=70°
b=140°
8) a=74°
b=106°
c=41°
d=115°
11305 is the volume of the red cylinder
7.5x + 40 = 70
Note the equal sign. What you do to one side, you do to the other. Isolate the x. Do the opposite of PEMDAS.
First subtract 40 from both sides
7.5x + 40 (-40) = 70 (-40)
7.5x = 70 - 40
7.5x = 30
Next, divide 7.5 from both sides
7.5x/7.5 = 30/7.5
x = 30/7.5
x = 4
4 friends are going to the aquarium together
hope this helps