2.

first let us find the equivalent resistance of the 3 resistors:

Rt = (1/15 + 1/15 + 1/15)^-1 = 5 ohm

now using ohms law we know that:

x / Rt = 2.5 ---> x = 12.5 [v]

3.

again using the same strategy, we first find the equivalent resistance of the circuit:

Rt = 5 + x/2

now using ohms law we know that:

24 / (5+x/2) = 1.5

<=> 16 = 5+x/2

<=> x = 22 [ohm]