Write out all of the equations you have. Which are the simplest looking equations? If you have an equation involving only two letters, can you write down the possible values those letters could take, knowing that each letter is a different number between \(1\) and \(9\)?
Can you spot any equations which have only one possible combination of numbers? For example, if \(a+b+c+d=10\), where \(a\), \(b\), \(c\) and \(d\) are whole numbers between \(1\) and \(9\), the only possible numbers are \(1+2+3+4=10\). Can you use this to narrow down the possible values for each letter?
Write down all of the equations and simplify them as much as possible. Can you spot any with similar letters in them? Can you use your knowledge of solving simultaneous equations with the techniques from the first Sudoku to solve the puzzle?