If company invest security in other company by 40% these securities valued using A- Fair value method B-Equity value method C- Consolidated method

As per the question, the investment qualifies for Investment in associates under IAS28 which states:

A holding of above20% and below50% of voting rights either directly or through subsidiaries will indicate significant influence and hence qualify for Associate company. A significant influence is the power to participate in financial and operating policy decisions but not to control them.

After we have identified the nature of investment, we can decide how to value the investment. According to IAS28 Investment in Associates: Investments are recorded according to Equity Accounting method where they are initially recorded at cost and are subsequently adjusted to reflect the investor's share of net assets of the Associate.