An investor divides a principal amount of $P$ dollars into two accounts. One account earns an annual interest rate of 4%, and the other account earns an annual interest rate of 6%. If $x$ dollars are invested in the account earning 4% interest, and the remaining amount is invested in the account earning 6% interest, which of the following expressions represents the total interest, in dollars, earned from both accounts after one year? (Assume no compounding.)