Sandy gets 3 marks for each correct sum and loses 2 marks for each incorrect sum. Sandy attempts 30 sums and obtains 45 marks. How many sums did Sandy get correct? Choose the correct choice from the following:
A) 18
B) 21
C) 24
D) 27
E) 28

Rationale: let x be the correct sums and ( 30 - x ) be the incorrect sums . 3 x - 2 ( 30 - x ) = 45 5 x = 105 x = 21 the answer is b .
Answer: B