I need an answer for this lolz

She worked 12 hours as a carpenter and 18 hours as a blacksmith

Step-by-step explanation:

You can solve this problem using a system of equations:

where c represents hours worked as a carpenter, and b represents hours worked as a blacksmith;

c + b = 30

20c + 25b = 690

To solve this system, you can multiply the first equation by 20 and subtract it from the second to isolate b:

  20c + 25b = 690

- 20c + 20b = 600

              5b  = 90

Now, you can solve for b:

5b = 90

b = 18 (divide both sides by 5)

Now that you know b, you can input it into the first equation to find c:

b + c = 30, where b = 18;

18 + c = 30 (replace b in the equation with 18 because of transitive property of equality)

c = 12 (subtract 18 from both sides of the equation))

people went from manufacturing one object at a time by hand to manufacturing many objects in factories