= Solution
Assume that each target's incorporated flux is proportional to its applied <power> over this operating range, and that the same composition convention is used throughout. The calibration gives $F_A/F_B=0.35/0.65$ at equal <powers>. Holding the A target unchanged while making the two incorporated fluxes equal therefore requires
$$
\boxed{P_B=30\frac{0.35}{0.65}=16.15\,\mathrm W}.
$$
The B <power> decreases because B originally supplies more material. This linear <magnetron sputtering> approximation neglects power-dependent yield, target condition, resputtering and changes in sticking probability. A second composition measurement is the experimental check.
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