Question 7

We can find the sum as follow.
We will arrange each value into ones and tens
42= 4 tens + 2 ones
0= 0 ones
6= 6 ones
Hence,

Also, we can use the commutative property of addition,
If we Re-write the expression as

For Question 8

We can re-group as

In both cases, we have 68 to be the answer.
We applied the Associative property of addition: Changing the grouping of the addends does not change the sum.