Explaining this example... (minimising variance)

Hi, i'm just wondering if someone could give me an explanation as to whats going on in this example. I don't understand why the values for E(X) and Var(X) would be involved in the equations if i'm asked to minimise Var(sY + tY).

Any insight as to whats going on would be greatly appreciated. (this is an example provided by my lecturer).


EDIT: Ignore this. Turned out the lecturer made a typo... in quite a few of his PDF's. He's issued corrected versions of most of em. Now the example makes sense. I'm beginning to believe i've been landed with a horrible lecturer :(
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