At a rate of 10 acres per day, he can plow his 55 acres of farmland in 55/10=<<55/10=5.5>>5.5 days.
At a rate of 12 acres per day, he can mow his 30 acres of grassland in 30/12=2.5 days.
Altogether, it would take him 5.5+2.5=<<5.5+2.5=8>>8 days to completely mow and plow his land.
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