Cost of debt

If company has taken a loan, but also given to the other company, will given loan's income reduce cost of debt in practice or we shouldn't take it into account? For example taken loan is $1000 10%, and given $500 also 10%, then when calculating cost of debt assuming tax rate is 15%, should we deduct from (1000*10%)-500*10%*(1-0.15) / 1000 or we should ignore interest income (1000*10%)*(1-0.15)/1000. Thank you.