a)\(50+\left(-12\right)+\left(-30\right)+12=\left(50-30\right)+\left(-12+12\right)=20+0=20\)
b)\(10^7:10^6-3^2.5=10^1-9.5=10-45=-35\)
c)\(514-4.\left\{\left[40+8.\left(6-3\right)^2\right]-12\right\}\)
\(=514-4.\left\{40+8.3^2-12\right\}\)
\(=514-4.\left\{40+72-12\right\}\)
\(=514-4.100\)
\(=514-400=114\)