Few questions related to Balance sheet and Income Statement?
1.) There is no logic in this question, because when there is an increase in net income for the year it will be in the form of something, ie it can be cash and cash equivalent like cash in hand or cash at bank. So as your ques says if there is increase in net income of 20 then asset side also increase by 20(cash) which makes the equation  Asset = liability + share capital tally 2.) Balance sheet is a statement of assets, liabilities, and capital of a business or other organization. Expenditure or income related items wont come under balance sheet it comes under profit and loss account 3.) Stockholders' equity can increase just as easy. When a firm issues bonus to the existing share holders from free reserve a/c or capital redemption reserve a/c or security premium this will increase the share holders equity and also decreases the reserve a/c