What is the variance of the number of heads that come up when a fair coin is flipped 10 times?

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So the answer to this is $5/2$.

I get that $E(x)=5$ which means that $\big(E(x)\big)^2 = 25$, therefore meaning that $E(x^2) = 55/2$.

How do I compute $E(x^2)$ in this scenario?