**Add up the following:**
* The probability that it lands on the red side exactly $4$ times is $\dbinom{6}{4}\cdot\dfrac{5^2}{6^6}=\dfrac{375}{46656}$
* The probability that it lands on the red side exactly $5$ times is $\dbinom{6}{5}\cdot\dfrac{5^1}{6^6}=\dfrac{30}{46656}$
* The probability that it lands on the red side exactly $6$ times is $\dbinom{6}{6}\cdot\dfrac{5^0}{6^6}=\dfrac{1}{46656}$
* * *
**Another way to look at it:**
* The total number of ways it can land is $6^6=46656$
* The number of ways it can land on the red side exactly $4$ times is $\dbinom{6}{4}\cdot5^2=375$
* The number of ways it can land on the red side exactly $5$ times is $\dbinom{6}{5}\cdot5^1=30$
* The number of ways it can land on the red side exactly $6$ times is $\dbinom{6}{6}\cdot5^0=1$
* * *
In either case, the probability of it landing on the red side at least $4$ times is $\dfrac{375+30+1}{46656}$