\[\boxed{\text{203\ (203).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[Выразим\ из\ формулы\ f:\]
\[c = \frac{5 \cdot (f - 32)}{9}\]
\[9c = 5 \cdot (f - 32)\]
\[f - 32 = \frac{9c}{5}\]
\[f = \frac{9c}{5} + 32.\]
\[\textbf{а)}\ если\ c = 4{^\circ}С:\]
\[f = \frac{9 \cdot 4}{5} + 32 = 7,2 + 32 =\]
\[= 39,2{^\circ}F.\]
\[если\ c = - 15{^\circ}С:\]
\[\ f = \frac{9 \cdot ( - 15)}{5} + 32 =\]
\[= - 27 + 32 = 5{^\circ}F.\]
\[если\ c = 0{^\circ}С:\]
\[f = \frac{9 \cdot 0}{5} + 32 = 32{^\circ}F.\]
\[\textbf{б)}\ если\ f = 20{^\circ}F:\]
\[c = \frac{5 \cdot (20 - 32)}{9} = \frac{5 \cdot ( - 12)}{9} =\]
\[= - 6\frac{2}{3}{^\circ}C.\]
\[если\ f = - 16{^\circ}F:\]
\[\ c = \frac{5 \cdot ( - 16 - 32)}{9} =\]
\[= \frac{5 \cdot ( - 48)}{9} = - 26\frac{2}{3}{^\circ}C.\]
\[если\ f = 0{^\circ}F:\]
\[\ c = \frac{5 \cdot (0 - 32)}{9} = \frac{5 \cdot ( - 32)}{2} =\]
\[= - 17\frac{7}{9}{^\circ}C.\]