Problem: if ( a – b ) is 15 more than ( c + d ) and ( a + b ) is 3 less than ( c – d ) , then ( a – c ) is :
Rationale: "( a – b ) – ( c + d ) = 15 and ( c – d ) – ( a + b ) = 3 = > ( a – c ) – ( b + d ) = 15 and ( c – a ) – ( b + d ) = 3 = > ( b + d ) = ( a – c ) – 15 and ( b + d ) = ( c – a ) – 3 = > ( a – c ) – 15 = ( c – a ) – 3 = > 2 ( a – c ) = 12 = > ( a – c ) = 6 answer : a"
annotated_formula: divide(15, 3)