Suppose that a firm is operating at a point off its expansion path, where MRTSLK >PL/PK Explain

Question:

Suppose that a firm is operating at a point off its expansion path, where
MRTSLK >PL/PK
Explain how this firm could increase its output without changing its total expenditure on inputs. Use this to give an additional argument for why a firm operating off its expansion path would want to move toward its expansion path.