Answer
$d=2\sqrt 2$
Work Step by Step
$a+bi=1+5i$ and $s+ti=-1+3i$
$d=\sqrt {(s-a)^2+(t-b)^2}=\sqrt {(-1-1)^2+(3-5)^2}=\sqrt {(-2)^2+(-2)^2}=\sqrt {4+4}=\sqrt 8=2\sqrt 2$
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