Samantha solved an equation, as shown below:

Step 1: 15r = 105
Step 2: r = 105 - 15
Step 3: r =90

Part A: Is Samantha's answer correct or incorrect? If it is incorrect, explain why it is incorrect and show the correct steps to solve the equation. (6 points)

Part B: How many solutions does this equation have? (4 points)