For f(x) = log(x+3) what is the base

Find the simple interest earned to the nearest cent for each principal,interest rate,and time 735 7% and two and a half years

When you answer this can you explain

Frank owns a $141,000 home, for which he has a 30-year mortgage in the amount of $700 a month. once he has paid off mortgage, how much will he have paid in investment? a. $111,000 b. $109,000 c. $120,000 d. $141,000