If an Increase of $10 Billion in Investment Results in an Increase

If an increase of $10 billion in investment results in an increase in equilibrium expenditure of $40 billion, the multiplier equals

A) $10 billion × $40 billion = $400 billion.
B) $10 billion - $40 billion = -$30 billion.
C) $10 billion ÷ $40 billion = 0.25.
D) $40 billion ÷ $10 billion = 4.
E) $40 billion - $10 billion = $30 billion.