To simplify the expression $5.3 + 6 \times 1.05 \div 2.1$, we need to follow the order of operations (PEMDAS/BODMAS):

1. Multiplication and Division (from left to right):

   • First, calculate $6 \times 1.05 = 6.3$.
   • Next, divide the result by $2.1$: $6.3 \div 2.1 = 3$.

2. Addition:

   • Now, add $5.3 + 3 = 8.3$.

So, the simplified result is: $8.3$

Would you like more details, or do you have any questions?

Here are some related questions:

1. How does the order of operations affect this calculation?
2. What happens if we change the numbers in the expression slightly?
3. Can you explain why we calculate multiplication and division before addition?
4. How can we solve similar expressions with more terms?
5. What if this expression included parentheses—how would that change the answer?

Tip: Remember, always perform multiplication and division before addition and subtraction unless parentheses indicate otherwise.