Savers make deposits and investments in order to earn what? Why don't savers invest their money directly with the businesses?

Savers make deposits and investment in order to earn interest on their money. This often works very well because they do not earn only interest as a percentage of their money, but also interest as a percentage of previously accrued interest, something known as compound interest.

Savers do not invest their money directly with the businesses because real economic activity tends to be riskier (although it could also be more profitable for this same reason). This is why they often prefer to invest the money on financial instruments.

answer decisions made by individual households and firms;

answer: marginal utility of the fourth brownie is 0.

explanation: marginal utility is the addtional utility gained from the consumption of one more unit of a good. it is given by,

so, marginal utility at the 4th unit will be given by

since, the values are not given here, you can simply find marginal utility at fourth unit by subtracting total utility at 3rd unit from total utility at 4th unit.