You have to plug in the values into the equation.
Since a=6, all the a's in the equation would be replaced by 6 and same goes for the b.
^ means exponent btw
= -[2(6)^2 -6- (5(6)^2-3(3)) -4(6)^2 +2(3)]
Calculate/ simplify
= -[2(36)-6 - (5(36) -9)-4(36)+6]
Multiply all the things in parenthesis
= -[72-6-(171)-144+6]
Add/subtract
= -[-243]
Negative times negative becomes positive therefore, the answer becomes 243