-21(4-10a)-54a

To simplify the expression \(-21(4 - 10a) - 54a\), follow these steps:

1. Distribute \(-21\) to both terms inside the parentheses: \[-21 \cdot 4 + (-21) \cdot (-10a) = -84 + 210a\]

2. Now, incorporate the \(-54a\) from the original expression: \[-84 + 210a - 54a\]

3. Combine like terms (the terms with \(a\)): \[210a - 54a = 156a\]

4. Put it all together: \[-84 + 156a\]

So, the simplified expression is: \[ 156a - 84 \]