Let \( x \) represent the number of minutes that have passed.
For the first vat that starts empty and fills at a rate of 6 gallons per minute, the amount of liquid in the first vat after \( x \) minutes can be expressed as:
\[ A_1 = 6x \]
For the second vat, which starts with 10 gallons and fills at a rate of 4 gallons per minute, the amount of liquid in the second vat after \( x \) minutes is:
\[ A_2 = 10 + 4x \]
To find out when the two vats will have an equal amount of liquid, we set \( A_1 \) equal to \( A_2 \):
\[ 6x = 10 + 4x \]
Now, we can solve for \( x \):
- Subtract \( 4x \) from both sides:
\[ 6x - 4x = 10 \]
- This simplifies to:
\[ 2x = 10 \]
- Now, divide both sides by 2:
\[ x = 5 \]
So, after 5 minutes, both vats will have an equal amount of liquid.