a) \(5.\left(-3\right)^2-14.\left(-8\right)+\left(-31\right)\)
\(=5.9+112-31\)
\(=45+112-31\)
\(=157-31\)
\(=126\)
b) \(6.\left(-2\right)^3+5.\left(-4\right)-\left(-12\right)\)
\(=6.\left(-8\right)+5.\left(-4\right)+12\)
\(=-48-20+12\)
\(=-68+12\)
\(=-56\)