在job matching problem中
U是unemployed worker预期收入的折现价值
W是employed worker预期收入的折现价值
r是利率
θq (θ)是unemployed worker转变为employed worker的概率
z是unemployed worker enjoy some real return z during searching a job

下面这个式子要怎么理解

rU = z + θq (θ) (W − U)
左边rU是指什么？右边 θq (θ) (W − U)要怎么理解呢？

谢谢