How does a company assess its sustainable growth rate (SGR)?

Question Text
How does a company assess its sustainable growth rate (SGR)?        How does a firm use the SGR in decision making?        What are the consequences for a firm that grows a higher rate than its SGR?        What are the consequences for a firm that grows at a lower rate than its SGR?  
Consider the following ideas to include in your answer:        Which variables are used in calculating the SGR?        How does a firm use the SGR in choosing a financing option?        How does a firm finance a growth that is higher than its SGR?        What is the opportunity cost for a firm that grows at a lower rate than its SGR?