She earns $20 per hour as a carpenter and $25 per hour as a blacksmith, last week Giselle worked bot

She earns $20 per hour as a carpenter and $25 per hour as a blacksmith, last week Giselle worked both jobs for a total of 30 hours, and a total of $690. How long did Giselle work as a carpenter and how long did she work as a blacksmith?

Assumptions:

• Let b be the number of hours Giselle worked as a blacksmith
• Let c be the number of hours Giselle worked as a carpenter

Givens:

1. b + c = 30
2. 25b + 20c = 690

Rearrange equation (1) to solve for b by subtracting c from each side:

1. b = 30 - c
2. 25b + 20c = 690

Substitute equation (1) into equation (2) for b
25(30 - c) + 20c = 690

Multiply through:
750 - 25c + 20c = 690

To solve for c, we type this equation into our search engine and we get:
c = 12

Now, we plug in c = 12 into modified equation (1) to solve for b:
b = 30 - 12
b = 18