Use Slater's rules with groups (1s), (2s,2p), (3s,3p), (3d), (4s,4p). Each other electron in the same group shields 0.35. For an $ns$ or $np$ electron, each electron in shell $n-1$ shields 0.85 and each deeper electron shields 1.00. For a $d$ electron, every electron in a lower group shields 1.00. Higher groups do not shield. For manganese ($Z = 25$), let $X = Z_{eff}$ (a $3d$ electron of $\text{Mn}^{2+}$) minus $Z_{eff}$ (a $4s$ electron of neutral Mn). Find $10X$. The answer is an integer, rounded to the nearest whole number.