Determine the number that must be subtracted from both terms of the ratio 43 : 91 to make the ratio 3 : 7.

Correct option is C

Given:
The ratio is 43:91.
The required ratio is 3:7.
Solution:
Let the number to be subtracted be x.
​$$\frac{43 - x}{91 - x} = \frac{3}{7} \\7(43 - x) = 3(91 - x) \\301 - 7x = 273 - 3x \\301 - 273 = 7x - 3x \\28 = 4x \\x = \frac{28}{4} \\x = 7$$​​
Thus, the number that must be subtracted from both terms is 7.