A is the answer i think so
To find the difference, subtract Thea's earnings from Hadley's earnings.
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Thea earned $54 more than Hadley.
A=$20.20/10gal=$2.02 per gal
B=$26.04/12gal=$2.17 per gal
C=$28.14/14gal=$2.01 per gal
D=$30.45/15gal=$2.03 per gal
So C is the cheapest per gallon.
Process efficiency is a measure of the ratio of process outputs to inputs.