Expanding the expression we get

(2)(4)+(2)(-j5)+(j3)(4)+(j3)(-j5)

Next we multiply the 4 products, pretending that j is an actual number.

8-j10+j12-j215

We replace j2 by -1.

8-j10+j12-(-1)15

Then we gather the real and imaginary terms.

(8+15)+j(12-10) = 23+j2

The result is the sum of the real number 23 and the imaginary number j2.

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