\[\boxed{\text{6.202.}}\]
\[\textbf{а)}\ x = 4\ и\ y = 3:\ \]
\[25,4x + 1,47y =\]
\[= 25,4 \cdot 4 + 1,47 \cdot 3 =\]
\[= 101,6 + 4,41 = 106,01.\ \]
\[x = 10\ и\ y = 100:\ \]
\[25,4x + 1,47y =\]
\[= 25,4 \cdot 10 + 1,47 \cdot 100 =\]
\[= 254 + 147 = 401.\ \]
\[\textbf{б)}\ a = 75\ и\ b = 10:\ \]
\[14,34a + 13,5b =\]
\[= 14,34 \cdot 75 + 13,5 \cdot 10 =\]
\[= 1\ 075,5 + 135 = 1\ 210,5.\ \]