Calculate the effective resistance across AB :

Explanation

Resistance of 3 `Omega ` is in parallel to series combination of 4 `Omega ` and 5 `Omega ` resistance, therefore sum of series resistance `R_(45) = 4 + 5 = 9 Omega `
For parallel combination of it with 3 `Omega ` resistance
`(1)/(R_p) = (1)/(R_3) +(1)/(R_(4.5 ))`
` therefore (1)/(R_p) = 1/3 +1/9 = 4/9`
` therefore R_p = 9/4 = 2.25 Omega `
` therefore ` Total resistance between A and B is give by
` R_(AB) =8 +R_p = 8 + 2.25 = 10.25 Omega `