The sum of 42 and 55, doubled

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).

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