1. **State the problem:** Simplify the expression $ (6b^2 - 4b^4) - (7b^2 - b^4) $. 2. **Rewrite the expression by distributing the minus sign:** $$ 6b^2 - 4b^4 - 7b^2 + b^4 $$ 3. **Group like terms:** $$ (6b^2 - 7b^2) + (-4b^4 + b^4) $$ 4. **Simplify each group:** $$ (6 - 7)b^2 + (-4 + 1)b^4 $$ $$ = -1b^2 - 3b^4 $$ 5. **Final simplified expression:** $$ -b^2 - 3b^4 $$ This means the expression simplifies to $-b^2 - 3b^4$. Note: The handwritten evaluation $13b^2$ and $3b^4$ is incorrect based on the original expression.