What is the w-4 form used for

Juan's investment portfolio was valued at $125,640 at the beginning of the year. during the year, juan received $603 in interest income and $298 in dividend income. juan also sold shares of stock and realized $1,459 in capital gains. juan's portfolio is valued at $142,608 at the end of the year. all income and realized gains were reinvested. no funds were contributed or withdrawn during the year. what is the amount of income juan must declare this year for income tax purposes?