Describe how to calculate the speed of a wave.

The speed of a wave can be calculated through v=fλ, where v is the speed of the wave, f is the frequency, and λ (lambda) is the wavelength.  Simply use the frequency times the wavelength to find the speed.  This is the simplest answer I can give; hope it helps!

Indoraptor for sure

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current