\(\frac{61/2}{20} = \frac{x}{81/8}\)
multiply the 2nd fraction by 8/8 to get rid of the 8 in the denominator:
\(\frac{61/2}{20} = \frac{8x}{81}\)
simplify the 1st fraction by multiplying by 2/2:
\(\frac{61}{40} = \frac{8x}{81}\)
now, you can cross-multiply:
\(61*81=40*8x\)
\(4941=320x\)
\(x=\frac{4941}{320}\) or \(15 \frac{141}{320}\)
