Answer:
30 new workers were brought in to join the crew
Explanation:
1 situation
15*12=x ( x is the full work)
2 situation
3*15+3*y=x
15*12=3*15+3*y
180=45+3*y
3y=180-45
3y=135
y= 135/3=45
y include the 15 person road crew that works from the beginning.
So, the new workers are 30. (45-30)