To get Second Number add $3$ to first number and to get third number subtract $2$ from second number and this process will continue.

$7+3=10$

$10-2=8$

$8+3=11$

$11-2=9$

$9+3=12$

$12-2=10$

Hence,$10$ is the Answer.

In the given series having 2 different series such as $7,8,9,10,…., 10,11,12,$. In the odd place, we put the first series term, even place we put the second series term. so the next term of the series should be $10$

Another way,

given series having the following patterns:

So the next term should be $10.$