(A) 0.3
Using the step-deviation formula: $\bar{x} = a + h\bar{u}$
$$64 = 62.5 + 5 \times \bar{u} \implies 5\bar{u} = 1.5 \implies \bar{u} = 0.3$$
The key formula is $\bar{x} = a + h\bar{u}$. Substitute the known values ($\bar{x} = 64$, $a = 62.5$, $h = 5$) and solve for $\bar{u}$. Many students mistakenly choose 0.5 (dividing 1.5 by 3) or 1.5 (forgetting to divide by $h$). Always isolate $\bar{u}$ by dividing the difference $(\bar{x} - a)$ by $h$.