-21•(4-10а)-54а

(-21) • (4 - 10a) - 54a

To solve this expression, we can simplify using the distributive property.

First, distribute -21 to both terms inside the parentheses: (-21) • 4 + (-21) • (-10a) - 54a

Simplify: -84 + 210a - 54a

Combine like terms: -84 + 156a - 54a

Combine like terms again: (-84) + (156a - 54a)

Simplify further: -84 + 102a

So, the answer is -84 + 102a.