\(\frac{1}{r} = \frac{1}{r_1} + \frac{1}{r_2}\)

= \(\frac{1}{5} + \frac{1}{20}\)

= \(\frac{4 + 1}{20} = \frac{5}{20}\)

r = \(\frac{20}{5}\)

= 4\(\Omega\)

R = R₁ + R₂

= 5 + 4

= 9\(\Omega\)

but V = IR

I = \(\frac{V}{R} = \frac{9}{9}\)

= 1A