a − [2b − {3a − (2b − 3c)}]
We will first remove the innermost grouping symbol ( ), followed by { } and then [ ].
∴ a − [2b − {3a − (2b − 3c)}]
= a − [2b − {3a − 2b + 3c}]
= a − [2b − 3a + 2b − 3c]
= a − [4b − 3a − 3c]
= a − 4b + 3a + 3c
= 4a − 4b + 3c