The unit’s place digit in ${\left(15\right)}^{550}$ is

We have ${\left(15\right)}^{550}$

In 15 (base) unit’s digit is 5

So ${\left(15\right)}^{550}$ last digit will be $5^{550}$ and we know $5^n\forall n\in N$ last digit 5

$\therefore$ Last digit (unit’s digit) of ${\left(15\right)}^{550}$ is 5