Read the following passage and answer the question.

Given the precarious condition of its ground and surface water resources (rivers, stream, lakes, wetlands and reservoirs). India could be a water-scarce country in the next 40 years. With 1,486 cubic meters (∼1.5 million litres) of water available per person, per annum. India falls in the water stressed category. A dip below 1000 cubic meters per person, per annum will push it into the waterscarce category.

The manner of water consumption also compounds the problem. Central Ground Water Board (CGWB) statistics show the indiscriminate use of ground water turned 4% of the total 7,809 assessed units in the country critical in 2022 while 14% were assessed as over-exploited. The situation was worse in 2017 when 17% of the units overexploited. Various recharge and conservation efforts have borne fruit but the number of such units remain high in state like Punjab, Rajasthan, Haryana, Delhi, Tamil Nadu and Karnataka.

In India, 87% of groundwater is extracted for irrigation and experts say excess withdrawal round the year may be the biggest reason for depletion, as the recharge primarily happens in the monsoon. On the other hand encroachment of water bodies and the discharge of untreated waster water into rivers and streams have reduced the surface water resources.

Assuming that the total number of ground units assessed by CWGB in the years 2017 and 2022 were same (i.e., 7089). What is the difference between the number of over-exploited units in 2017 and 2022?