digital to analogue question?

Question

5bit DAC has a voltage o/p for a binary input 10100 an o/p voltage 12mV produced find the proportinality and hence the o/p voltage when the binary input is 11100

Answer 1

16.8 mV
I mentally converted 10100 to 20(decimal) and
11100 to 28(decimal) and made a proportion out
of the figures.
20/12=28/x becomes
x=12(28)/20
x=16.8

Answer 2

Assuming the response of the DAC is linear...
10100 = 0x14 = 20d -> 12mV
11100 = 0x1c = 28d
Proportionality: 12mV / 20 = 0.6mV per bit.
Output voltage: 12 * 28 / 20 = 16.8