Where's the computer? — .（在窗户旁边）
A：It's near the window.
B：It's near the desk.
5x－3.5x=0.9
x=____
将电阻为R1=3Ω的导体与电阻为R2的导体串联后总电阻为9Ω，则R1与R2并联后总电阻是
