You can put this solution on YOUR website! The mean is 2(mean of x)+1 or 11
the variance is the square of the coefficient or 4 times the variance of the original.
The sd of the original was 4, so its variance was 16 and the new variance is 64 with a sd of 8
y is distributed normally with mean of 11 and sd of 8.
z=(x-mean)/sd
so z for the low end is (8-11)/8 or -3/8
and for the high end is (13-11)/8 or +1/4
for z to be between these two values gives a probability of 0.2449
