Hello my name is Jeff (sorry)
Answer:
The correct option is (d)-He wrote commutative instead of associative in Step 2.
Step-by-step explanation:
Commutative property: 
Associative property:
Now consider the provided expression.
(6.2 − 1.6) − 4.4 + 7.8
Step 1
(6.2 − 1.6) − 4.4 + 7.8
Step 2 Use Associative property
6.2 + (−1.6 − 4.4) + 7.8
Step 3: Simplify
6.2 − 6 + 7.8
Step 4: Use commutative property
14 − 6
Step 5: Simplify
14 − 6 = 8
Hence, the wrong step is step 2. He wrote commutative instead of associative in Step 2.
Therefore, the correct option is (d)-He wrote commutative instead of associative in Step 2.
Answer: 8.7 x 5.28
We have to find that expression , which has an estimated product of
1.→44.7 x 2.1
2.→7.5 x 8.4
3.→8.7 x 5.28
4.→38.1 x 7.3
We will start from option 1.
→44.7 x 2.1
44.7 when estimated to nearest tenth=45
2.1, when estimated to nearest tenth=2
44.7 × 2.1=45×2=90
Option 2
7.5 x 8.4
7.5 when estimated to nearest tenth=8
8.4, when estimated to nearest tenth=8
⇒7.5 × 8.4=8×8=64
Option 3
8.7 × 5.28
8.7, when estimated to nearest tenth=9
5.28, when estimated to nearest tenth=5
⇒8.7 × 5.28=9×5=45
Option D
38.1 × 7.3
38.1 when estimated to nearest tenth=38
7.3, when estimated to nearest tenth=7
⇒38×7=266
Option C:⇒8.7 × 5.28 has an estimated product of 45