Solve the following addition problems using the regrouping method: a) 65 + 52, b) 76 + 63, c) 86 + 65

$65 = 6$ tens and 5 ones.
$52 = 5$ tens and 2 ones.

Total ones: $5 + 2 = 7$ ones.
Total tens: $6 + 5 = 11$ tens.

Since there are 11 tens, we can regroup 10 tens into 1 hundred.
11 tens $= 1$ hundred and 1 ten.

We have 1 hundred, 1 ten, and 7 ones.

The sum is $\boxed{\text{117}}$.

$76 = 7$ tens and 6 ones.
$63 = 6$ tens and 3 ones.

Total ones: $6 + 3 = 9$ ones.
Total tens: $7 + 6 = 13$ tens.

Since there are 13 tens, we can regroup 10 tens into 1 hundred.
13 tens $= 1$ hundred and 3 tens.

We have 1 hundred, 3 tens, and 9 ones.

The sum is $\boxed{\text{139}}$.

$86 = 8$ tens and 6 ones.
$65 = 6$ tens and 5 ones.

Total ones: $6 + 5 = 11$ ones.
Total tens: $8 + 6 = 14$ tens.

Since there are 11 ones, we can regroup 10 ones into 1 ten.
11 ones $= 1$ ten and 1 one.

We started with 14 tens and added 1 ten from the regrouped ones, making a total of $14 + 1 = 15$ tens.
Since there are 15 tens, we can regroup 10 tens into 1 hundred.
15 tens $= 1$ hundred and 5 tens.

We have 1 hundred, 5 tens, and 1 one.

The sum is $\boxed{\text{151}}$.