Answer: B. -10 weeks
Step-by-step explanation: You start by writing the equation:
400 + 15w = 250 + 25w
Then you solve.
First, you subtract 15w on both sides of the equation and end up with 15w;
400 + 15w = 250 + 25w
- 15w -15w
400 = 250 + 15
Second, you subtract 400 from both sides of the equation and end up with -150;
400 + 15w = 250 + 25w
- 15w -15w
400 + 15w = 250
- 400 - 400
15w = -150
Lastly, you divide 15 from both sides of the equation (canceling out 15, leaving the w) and get -10;
400 - 15w = 250
-400 -400
15w = -150
/15 /15
w = -10