Solve the system of equations. -4x+7y = 20 & y=3x+15 solve for x and y using substitution

The life (in hours) of a magnetic resonance imagining machine (mri) is modeled by a weibull distribution with parameters β = 2 and δ = 370 hours. (a) determine the mean life of the mri. (round your answer to 2 decimal ) determine the variance of the life of the mri. (round your answer to 1 decimal ) what is the probability that the mri fails before 250 hours? (round your answer to 4 decimal places.)