Original vision in left eye = 74%.
It increased by 11%.
His improved vision = 74 + (11% of 74) = 82.14%
Original vision in right eye = 66%
It increased by 12%
His improved vision = 66 + (12% of 66) = 73.92%
His overall vision after improvement = 82.14% × 73.92% = 60.71%