The return on the Rush Corporation in the state of recession is estimated to be -21% and the return on Rush in the state of boom is estimated to be 30%. The return on the Oberman Corporation in the state of recession is estimated to be 45% and the return on Oberman in the state of boom is estimated to be -18%. Given this information, what is the covariance between Rush and Oberman if there is a 0.50 probability that the economy will be in the state of boom and a 0.50 probability that the economy will be in the state of recession.