-4 (x - 5) + 3 (a - 7)
First, expand your problem. / Your problem should look like: -4x + 20 + 3a - 21
Second, simplify. / Your problem should look like: -4x + 3a - 1
Answer: -4x + 3a - 1 (C)
Thickest to thinnest....
0.33m , 0.3mm, 0.275mm, 0.25mm
Assuming that each marble can be picked with equal probability, we notice that there is a total of

marbles, of which 2 are red.
So, the probability of picking a red marble is

In fact, as in any other case of (finite) equidistribution, we used the formula
