Salary vs. Commissions $6K $5K y = 0.0987x - 844.51 $4K Commissions last quarter $3K $2K $1K $0 $10K $20K $30K $40K $50K $60K Base salary First, you plot this quarter's commissions against each salesperson's base salary and add a trend line. Match these terms to their counterparts. slope $3,202 quarterly commissions predicted for $41,000 base salary $6,064 quarterly commissions y-intercept predicted for $70,000 base salary interpolation a corrective factor of -844.51 for every extra dollar of base extrapolation salary, commissions see a 9.87 cent increase