Question

how will you connect three 13 ohm resistor to get 39 and 19.5​

Answer 1

To get 39Ω, resistors must be connected in series connection.

Rs= R1 + R2 + R3

   =13 + 13 + 13

   = 39Ω

To get 19.5Ω, two resistors must be connected in parallel and that combination must be connected in series to the third resistor.

1/Rp= 1/R1 + 1/R2

      = 1/13 + 1/13

      = 2/13

Rp= 13/2

Rs= Rp + R3

   = 13/2 + 13

   =13+26/2

   =39/2

   =19.5Ω

:D