The answer is the second choice. Hope that was helpful
I think it may be 1,680B but I'm not too sure...
We are given that there are a total of 78 students. If we set the following variables:

Then, the sum of all of these must be 78, that is:

Since there are 15 in chemistry and physics and 47 in chemistry, we may replace that into the equation and we get:

Simplifying:

Now we solve for P by subtracting 62 on both sides:

Therefore, there are 16 students in physics
.05n + .10d = 4.85
n - 34 = d
Substitute the second equation into the first equation and solve for n.
.05n + .10(n - 34) = 4.85
.05n + .10n - 3.4 = 4.85
combine like terms
.15n - 3.4 = 4.85
add 3.4 to both sides
.15n = 8.25
divide both sides by .15
n = 55
d = n - 34
d = 55 - 34
d = 21
CHECK
21 * .1 = 2.10
55 * .05 = 2.75
2.10 + 2.75 = 4.85
21 dimes and 55 nickels