a) 16abc: (8a); б) 24pqr: (-4pq); в) -42cdm: (12c); г) -99xyz: (-9x).

a) 16abc ∶ (8a) = (16 ∶ 8) × (a ∶ a) × b × c = 2 ∙ 1 ∙ b ∙ c = 2bc

б) 24pqr ∶ (−4pq) = (24 ∶ (−4)) × (p ∶ p) × q × (r ∶ 1) = −6 ∙ 1 ∙ q ∙ r = −6qr

в) −42cdm ∶ (12c) = (−42 ∶ 12) × (c ∶ c) × d × m = −3,5 ∙ 1 ∙ d ∙ m = −3,5dm

г) −99xyz ∶ (−9x) = (−99 ∶ (−9)) × (x ∶ x) × y × z = 11 ∙ 1 ∙ y ∙ z = 11yz

Ответ: a) 2bc; б) -6qr; в) -3,5dm; г) 11yz