Below is an instruction that describes a task. Write a response that appropriately completes the request in English. Please answer in English.

### Instruction:
Rodney is a door-to-door salesman trying to sell home security systems. He gets a commission of $25 for each system he sells. He is canvassing a neighborhood of four streets with eight houses each. The first street gave him half the sales that the second street did, while every house on the third street turned him away and the fourth street resulted in only one sale. His total commission was $175. How many security systems did he sell on the second street?

### Response:
Let S be the number of systems Rodney sold on the first street.
He sold twice as many on the second street, so he sold 2S systems there.
Based on his commission, he sold 175 / 25 = <<175/25=7>>7 systems.
He sold 1 system on the fourth street, so in total, he sold S + 2S + 0 + 1 = 3S + 1 = 7 systems.
Thus, Rodney sold 3S = 7 - 1 = 6 systems on the first and second streets.
Therefore, on the first street, Rodney sold S = 6 / 3 = <<6/3=2>>2 systems.
On the second street, Rodney sold 2 * 2 = <<2*2=4>>4 security systems.
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