Log Utiliy Function Trick
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$$0.75/p_xx= 0.25/p_yy$$

Multiply both sides by $p_xx p_yy$, you get:
$$0.75p_yy=0.25p_xx$$

Add $0.75p_xx$ to both sides, you get:

$$0.75(p_xx+p_yy)=p_xx$$

So:
$$\frac{p_xx}{p_xx+p_yy}=0.75=\frac{3}{4}$$

And you spend the rest of your budget, so $1/4$ of it, on $y$.