You should refer to HS283
as part of this answer.
Had you returned to live in the property before you sold it, you could have got exemption from CGT for the period you lived and worked abroad under the "absence relief" rules as well as for the period you lived in it. That's assuming you didn't buy a home abroad.
As far as the expenses are concerned, you can only add the cost of improvements to the cost of the property. Repair costs are only deductible from rental income.
All is not lost however.
You made a gain of £55,500 when you sold the property (£143,000 - £87,500). You can reduce that further by deducting legal fees, survey fees, stamp duty, selling agent fees etc. You owned the property for 150 months of which you lived in it for 72 and let it for 78.
The gain for the period that you occupied the property will be exempt from CGT as will the gain for the last 18 months of ownership. That accounts for £33,300 (£55,500 / 150 x 90). The balance of the gain of £22,200 would normally be taxable but it will be covered by letting relief of £22,200 (the lesser of £40,000, £33,300 and £22,200). There will be no CGT to pay.
I hope this helps but let me know if you have any further questions.