$$ Total\ gallons=4 $$

$$ gallons\ used\ by\ Lyle=\frac{1}{2} $$

$$ gallons\ used\ by\ Ming=1\frac{1}{4} $$

$$ \therefore Total\ Gallons\ left=4-\frac{1}{2}-1\frac{1}{4}=2\frac{1}{4} $$