I agree with the others, you need to review some basic accounting!
Capex is the $ spent to build/acquire + maintain assets
Opex is the ongoing cost of running a product, business, or system
Interest rates on loans are essentially your cost of capital, and have intrinsic annual costs.
Furthemore, the way in which you reduce capex and opex totally depends on the industry and firm in question! We could close a few factories, renegotiate with suppliers, cut our labor force, pay out people less, etc. etc. (there are almost infinite options). We require much more context.