Ok i believe it would be D
The answer is -12g-3f-4. Hope this helps!
when running a line, in a right-triangle, from the 90° angle perpendicular to its opposite side, we will end up with three similar triangles, one Small, one Medium and a containing Large one. Check the picture below.

60 blocks in 30 min
18 blocks in 9 min
Method 1
60-18 = 42
42 blocks in 21 min
Method 2
30-9 =21 min
Answer:
-0.3 with a line on top of the 3