Mean, x̅=(4+6+8+9+9+10+12)/7=58/7=8.2857...
Taking this as a sample we need the variance s2=∑(x-x̅)2/6=6.9048, s (sample standard deviation)=2.628 approx.
We need the critical t value for 7-1=6 degrees of freedom for 2-tail 95%=2.447.
CI=8.29±2.447×2.628=8.29±6.43.