Answer:

A. 68

Step-by-step explanation:

Let x be the number of problems he can answer

Use ratio and proportion

12:3/4 = x: 4 1/4

3/4x = 12(4 1/4)

3x = 4(12)(4 1/4)

3x = 48(17/4)

3x = 12(17)

3x = 204

x = 204/3

x = 68