a, `18/5 xx 7/2 + 7/2 xx 2/9 + 7/2`
`= 7/2 xx ( 18/5 + 2/9 + 1 )`
`= 7/2 xx ( (18xx9)/(5xx9) + (2xx5)/(9xx5) + 45/45 )`
`= 7/2 xx ( 162/45 + 10/45 + 45/45 )`
`= 7/2 xx (162+10+45)/45`
`= 7/2 xx 217/45`
`= (7xx217)/(2xx45)`
`= 1519/90`
b, `17/2 xx 3/5 + 3/5 xx 1/2 + 3/5`
`= 3/5 xx ( 17/2 + 1/2 + 1 )`
`= 3/5 xx ( 17/2 + 1/2 + 2/2 )`
`= 3/5 xx (17+1+2)/2`
`= 3/5 xx 20/2`
`= 3/5 xx 10`
`= (3xx10)/5`
`= 30/5`
`= 6`