An electronic device has three batteries, but uses only one of the batteries at any given time. The remaining batteries serve as backups. When one battery fails, the device will begin using one of the backup batteries. The device will fail when all three of the batteries have failed. Let T1, T2, and T3 be continuous random variables representing the lifetimes of each of the three batteries, measured in days. Assume that these random variables are pairwise independent, and that each of them follows an exponential distribution with a mean of 215 days. Let L be a continuous random variable representing the lifetime of the device. Find P[L < 945]. 0.7329 0.6922 0.8143 0.8550 0.7736