Can you solve it?

$50^2$ and $100^2$ both end in 0, hence last digit is determined by $5^3$ which is $5$ since 5 raised to any power always end in 5!!

$50^2+100^2+5^3=12625$

${50}^2$ ends in $0$ . ${100}^2$ ends in $0$ . $5^3$ ends in $5$ . So, the last digit of this sum is $\color{#69047E}{\boxed{5}}$ .