rednet.open("left")
while(true) do
    num, msg, dist = rednet.receive()
    if msg == "7x2" then
        x, msg, y = rednet.receive()
        if msg == "on" then
            redstone.setOutput("back",true)
        else
            redstone.setOutput("back", false)
        end
    else
        rednet.receive()
    end
end