For these two questions, first you need to know that the voltage across each branch of a parallel circuit is the same.
So, for Q5, we can first find out the voltage across R₂ by V=IR.
Voltage across R₂ = 2.5 × 8 = 20V
Since R₂ and R₃ are in parallel circuit, their voltage should be the same. Thus, voltage across R₃ is 20V.
So, by V=IR,
current of R₃ = [tex]\frac{20}{4}[/tex] = 5A
Q6. voltage across R₁ = 2 × 4 = 8V
∴voltage across R₂ = 8V
current of R₂ = [tex]\frac{8}{8}[/tex] = 1A
Alternative method
From these two examples, you can find out that the current of each branch of the parallel circuit is inversely proportional to the resistance of the branch.
ie. for Q5,
[tex]\frac{R2}{R3}[/tex] = [tex]\frac{I3}{I2}[/tex]
[tex]\frac{8}{4}[/tex] = [tex]\frac{I3}{2.5}[/tex]
I₃ = 5A
Q6. [tex]\frac{R1}{R2}[/tex] = [tex]\frac{I2}{I1}[/tex]
[tex]\frac{4}{8}[/tex] = [tex]\frac{I2}{2}[/tex]
I₂ = 1A
