Need help on this plz

Look at arnold's attempt to solve the equation for b: 3b = 12 b = 3 · 12 b = 36 describe the mistake that arnold made.

When you answer this can you explain

Beth divided 9 ounces of her granola recipe into 4 equal-sized amounts. she placed the amounts into individual bowls. the fraction 9/4 represents the number of ounces of granola in each bowl. which other number represents the amount of granola beth has in each bowl? (a) 1 1/4 (b) 2 1/4 (c) 1 3/4 (d) 3 3/4 i need !