According to HDB's second quarter of 2021, the median price for 4-room HDB flats in Yishun was $426,500.
The asking price for this flat is $520,000.
Therefore, the expected cash-over-valuation will be around $93,500.
We advise you to check with the agent marketing the unit here: https://www.propertyguru.com.sg/listing/hdb-for-sale-512c-yishun-street-51-23627360
Hope this answers your question.