a) 4x³-9x³+7x³=
b) 5x²y³z⁴+x²y³z⁴-3x²y³z⁴=
c) 11x⁸-17x⁸+9x⁸-x⁸=
d) -14xy⁴-17xy⁴+3xy⁴=
e) 18xy³z⁵-20xy³z⁵+7xy³z⁵=​