Question: Let X be a gamma random variable with $\displaystyle \mu$ = 21 and $\displaystyle \sigma^2$ = 63. Find P(18$\displaystyle \leq$X$\displaystyle \leq$30).

I have calculated that $\displaystyle \beta$=3 and $\displaystyle \alpha$=7

but I'm not sure how to turn the interval 18 to 30 into some interval I can find in the tables.

Can you help?