A because the 6 and 3 cancel out
Then 2 x 8 is (16) and 15 x 5 is (75)
Making it A
I think it is 640.. What they mean is every inch equals 4 feet so you would multiply 8*4 and 5*4 then you get 32 and 20.. im sure you know area but just incase its base times height so 32*20=640
X=9
3x-12=x+6
2x-12=6
2x=18
X=9
The event that either M1 or M2 fails has probability

by the addition rule. Failure events are independent, so

so that

Denote this probability by
. Then
follows a geometric distribution with this parameter
and has density

The expectation is
.