Answer:
4500
so, have a good day, and um, i think i got this right, if not sry.
Neither A, B or D explains why plane is undefined. All 3 of those answers describe something about plane which is true. Plane indeed can be named using three non collinear points. However, B is telling why plane is undenified. I it described generally, not using a formal definition.
Answer is B
Answer:
$180
Step-by-step explanation:
Since the cost of the telescope with the 30% discount is $126 then $126 is 70% of the original price. Remember 100-30=70. To find the original price set up a proportion with these values:

Solve for the original price by cross multiplying numerator with denominator.
x(70) = 126(100)
70x = 12600
x= $180
This is quite simple, take 24 and divide it by four to get 6 now all you do is multiply 6 by 7 to get 42 so there are 42 blue marbles.