First, combine like terms on the right hand side: 3a+4b=2a−6b+24
Then we rearrange the equation so that all the terms with b in it are on one side, and the rest (a terms and constants) are on the other side. So now we have −10b=a−24
Since we want to get b on its own, we divide by −10b.
Thus b=−a−2410
Hope that helped!