Answer:
12 units
Step-by-step explanation:
Each side of the triangle is 1 unit. When putting 10 triangles together in figure 10, there will be 12 sides on the perimeter. Therefore, your answer is 12 units.
Eighths and their multiples are common fractions which I recommend memorizing, but to actually solve this, you use the literal meaning of a fraction and divide 5 by 8. See the long-division below (it was surprisingly difficult to type, so I hope it helps!).
To round 0.625 to the nearest hundredth, we go to the second decimal place, which is 5, so we round up to 0.63.
The third option is the right one