The state of idaho issued $2,000,000 of seven percent coupon 20 year semiannual payment tax exempt bonds five years ago. the bonds had five years of call protection but now the state can call the bonds if it chooses to do so. the call premium would be five percent of the face amount. today15 year five percnt seminannual payment bonds can be sold at par but foltation costs on this issue would be two percent. what is the net present value of the refunding ?

I need the formula please