Final answer:
Total assets must have increased by $100,000, reflecting the combined increase in total liabilities and stockholders' equity during the period.
Step-by-step explanation:
If total liabilities increased by $75,000 and stockholders' equity increased by $25,000 during a period, then total assets must have increased by the sum of these two amounts. According to the accounting equation, Assets = Liabilities + Stockholders' Equity, any change in liabilities or equity must be mirrored by an equal change in assets. Therefore, the total assets must have increased by $100,000.