Answer:
21 minutes
Step-by-step explanation:
30%=9
10%=3
100%-30%=70%
7×10%=70%
3x7=21
=21minutes
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.
Yes. 6/16 simplifies to 3/8, which is the same amount of people singing.
X times -3= a
i think thats it
D commutative property
Hope it helps