`1990 + 720 : ( a - 6 ) = 2710`
` 720 : ( a - 6 ) = 2710 - 1990`
` 720 : ( a - 6 ) = 720`
`a-6=720:720`
`a-6=1`
`a=1+6`
`a=7`
`=> 720 : ( a - 6) = 2710 - 1990`
` 720 : ( a - 6) = 720`
` a - 6 = 720 : 720`
` a - 6 = 1`
` a = 1 + 6`
` a = 7`
`1990 + 720 : ( a - 6) = 2710`
`=> 720 : ( a - 6) = 2710 - 1990`
`=> 720 : ( a - 6) = 720`
`=> a - 6 = 720 : 720`
`=> a - 6 = 1`
`=> a = 1 + 6`
`=> a = 7`
\(1990+720:\left(a-6\right)=2710\)
\(720:\left(a-6\right)=2710-1990\)
\(720:\left(a-6\right)=720\)
\(a-6=720:720\)
\(a-6=1\)
\(a=6+1\)
\(a=7\)