If y varies directly as x, and y is 20 when x is 4, what is the constant of variation for this relation?

7x+8y=-18, 4x-9y=-3 solve the system of equations

Need on this one asap im almost done with this subject

Eliza wants to make $10,000 from her investments. she finds an investment account that earns 4.5% interest. she decides to deposit $2,500 into an account. how much money will be in her account after 14 years?