`-8/18-15/27=-4/9-5/9=-9/9=-1`
`(9/25-2.18):(3 4/5+0,2)`
`=(9/25-36):(19/5+1/5)`
`=-891/25 :4`
`=-891/100`
`3/8. 19 1/3-3/8. 33 1/3`
`=3/8(19 1/3-33 1/3)`
`=3/8. (-14)`
`=-21/4`
`15/12+5/13-3/12-18/13`
`=(15/12-3/12)-(18/13-5/13)`
`=1-1=0`
`13/25+6/41-38/25+35/41-1/25`
`=(13/25-38/25-1/25)+(6/41+35/41)`
`=-26/25+1`
`=-1/25`
`4/5:(7/2+1/4)^2`
`=4/5: (14/4+1/4)^2`
`=4/5:(15/4)^2`
`=4/5: 225/16`
`=4/5. 16/225`
`=64/1125`
`x^2=16`
`<=> x^2=(+-4)^2`
`<=> x=+-4`