What is the Z-score and Probability to this question

If we make the assumption that U.S household daily checking account balances are normally distributed with a mean account balance of $520 and a standard deciation of $250 please indicate the following:

What is the Probability of selecting a household at random that possesses a checking account containing between $300 and $400?
Z-score(s)__________
Probability__________

What is the probability of selecting a household at random that possesses a checking account containing less than $300 OR more than $400?
Z-score(s)________
Probability_________

ANY help means ALOT! homework

z = (x − µ)/σ = (300 − 520)/250 = -.88
z = (x − µ)/σ = (400 − 520)/250 = -.48
P(-.88 < z < -.48) = normalcdf(-.88,-.48) ≈ .12618

z = -.88
z = -.48
P(z < -.88 or z > -.48) = 1 − P(-.88 < z < -.48) = 1 − .12618 ≈ .87382