The expression that represents the number of days until only 10% remains is
T((d) 10%) = 100 • (1/2)^3.322
19 is the answer because you just divided 228 by 12
D.) It is not correct because the second number tells you how far to go up or down, not across.
Second number represents y-coordinates, so they are the points in vertical direction, in that case you can't move in x-axis which is horizontal.
Hope this helps!