solve this

For the rule of 78, for a 12-month period, the last term in the sequence is 12 and the series sums to 78. for an 10 month period, the last term is and the series sum is . for a 15 month period, the last term is and the series sum is . for a 20 month period, the last term is and the series sum is

(-y to the power of 2 - 4y- to the power of 2 -6 y +3)

Solve the system of equations. 2x-2y=-4 and x+y=8. show work