Let's solve this step-by-step to identify the first incorrect line.
1. Line 1: [tex]\(21 + 35 \div 7 + 6(2)\)[/tex]
- According to the order of operations (PEMDAS/BODMAS), we first handle division and multiplication before addition.
- Perform the division [tex]\(35 \div 7\)[/tex], which equals 5.
- Perform the multiplication [tex]\(6 \times 2\)[/tex], which equals 12.
- So, substituting back into the expression, we get: [tex]\(21 + 5 + 12\)[/tex].
2. Line 2: [tex]\(21 + 5 + 6(2)\)[/tex]
- This line correctly simplifies [tex]\(35 \div 7\)[/tex] to 5, but it should also simplify [tex]\(6(2)\)[/tex] to 12.
3. Line 3: [tex]\(21 + 11(2)\)[/tex]
- This is where the mistake occurs. It mistakenly adds 6 and 5 to get 11 before multiplying by 2.
- Instead, Line 3 should have been: [tex]\(21 + 5 + 12\)[/tex].
Since the mistake was first introduced in Line 3, the first incorrect line is:
3
