Norton's theorem states that a complex network connected to a load can be replaced with an equivalent impedance

For maximum power transfer between two cascaded sections of an electrical network, the relationship between the output impedance Z₁ of the first section to the input impedance Z₂ of the second section is

A source v_s(t) = V cos 100 $$\pi$$t has an internal impedance of (4 + j3) $$\Omega$$. If a purely resistive load connected to this source has to extract the maximum power out of the source, its value in $$\Omega$$ shoud be