Two alternate resistors connected to a circuit have voltages of 6.4+ 5i and 7 - 4.21. What is the total voltage of the circuit?

What is the explicit formula for this sequence? -7, -4, -1, 2, a.) an = 8 + (b - 1)3 b.) an = -7 + (n - 1)3 c.) an = 3 + (n -1) (-7) d.) an = -7 + (n - )