Jason joined the military when he turned 18.  It took him 8 years to raise to the rank of chief.  Then 25% longer than that to go from chief to master chief.  He then spent 10 years more in the military before retiring.  How old was he when he retired?
It took 8*.25=2 years longer to go from chief to master chief than to get chief
So it takes him 8+2=10 years to become a master chief
That means he took 10+8=18 years to reach master chief from enlisting
So he was in the military for 18+10=28 years
So he was 28+18=46 when he retired