`a, 56/75 xx 50/42 + 17/25 : 34/15`
`= 8/9 + 17/25 xx 15/34`
`= 8/9 + 3/10`
`= 80/90 + 27/90`
`= 107/90`
`b, 3 2/3 : 2 3/4 + 9/12 xx 8/27 - 1 1/6`
`= 11/3 : 11/4 + 2/9 - 7/6`
`= 11/3 xx 4/11 + 2/9 - 7/6`
`= 4/3 + 2/9 - 7/6`
`= 24/18 + 4/18 - 21/18`
`= 28/18 - 21/18`
`= 7/18`
`c, 60/75 xx 25% : 3/5 - 2/15`
`= 4/5 xx 1/4 xx 5/3 - 2/15`
`= 1/5 xx 5/3 - 2/15`
`= 1/3 - 2/15`
`= 5/15 - 2/15`
`= 1/5`
`d, ( 126% - 8% ) : 4 + 12,05`
`= 118% : 4 + 1205/100`
`= 59/50 xx 1/4 + 1205/100`
`= 59/200 + 1205/100`
`= 59/200 + 2410/200`
`= 2469/200`