In the figure, 5Ω and 4Ω are in series, So their resultant will be 5+4 i.e. 9Ω.
Now, 9Ω and 3Ω are in parallel, so their resultant RP is calculated as :
‌

1

RP

‌=‌

1

9

+‌

1

3

‌

1

RP

‌=‌

1+3

9

‌

1

RP

‌=‌

4

9

∴‌‌RP=‌

9

4

=2.25Ω
Now, 8Ω and 2.25Ω are in series,
∴‌RAB‌=8+2.25
‌=10.25Ω