At the end of year X, automobile installment credit accounted for 36% of all outstanding consumer installment credit. At that time automobile finance companies extended $75 billion of credit, or 1/2 of the automobile installment credit. How many billion dollars of consumer installment credit was outstanding at that time?  Choose the most appropriate option.
A) 412.16	B) 150	C) 400	D) 416.67	E) 420.34

Rationale: "system of equations a = ( 36 / 100 ) c ( 1 / 2 ) a = 75 - - > a = 150 substitution 150 = ( 36 / 100 ) c c = ( 100 / 36 ) 150 calculate 150 / 36 * 100 the correct answer is d - the correct answer will be slightly smaller than 513 . therefore , the correct answer is 475 ."
Answer: D