Y-bus diagonal elements ($Y_{ii}$) represent the sum of all admittances connected to bus $i$.

Adding an admittance between two nodes changes both the diagonal elements ($Y_{ii}$ and $Y_{jj}$) and the off-diagonal elements ($Y_{ij}$ and $Y_{ji}$).

Calculations are performed by adding complex numbers in rectangular form $a + jb$.

Simplifies power flow analysis calculations.

Easily handles network modifications without recalculating the entire matrix.

Requires complex number arithmetic which is prone to manual calculation errors.

Applicable only to linear network components.

Power flow studies (Newton-Raphson, Gauss-Seidel).

Short circuit analysis and contingency studies.

The calculation: $(1.018 + 2) - j(3.054 + 6) = 3.018 - j9.054$.

Option C is the only mathematically consistent result for the stated operation.