If you truly cannot pay, do not pirate. There are excellent, safe, free alternatives on the Play Store:

Why is "Pro Electronics Tools Mod APK" such a high-volume keyword?

Features automated solvers for Ohm's Law, resistor/inductor color codes, SMD markings, voltage dividers, and series/parallel configurations.

You do not actually need an APK. Websites like or OhmLawCalculator.com work perfectly in Chrome on your phone. Save them to your home screen as a "Web App." They work offline, have no malware, and are completely free.