\[\boxed{\mathbf{2.}\mathbf{189}}\]
\[\textbf{а)}\ 0,5^{2} - 0,4^{2} =\]
\[= 0,25 - 0,16 = 0,09\]
\[\textbf{б)}\ 4^{3} - 14,5 = 64 - 14,5 = 49,5\]
\[\textbf{в)}\ 0,6^{2} \cdot 7 = 0,36 \cdot 7 = 2,52\]
\[\textbf{г)}\ 3,9\ :0,1^{3} = 3,9\ :0,001 =\]
\[= 3900\ :1 = 3900\]