I keep getting this nuclear chem problem wrong. Can someone help me?

Barium-140 (t1/2 = 12.8 d) released in the fire at the Chernobyl nuclear plant has been found in some agricultural products in the region. The biological half-life of barium-140 in the human body is 65 d. What is the effective half-life of barium-140? The biological half-life of a radioisotope is the time required for the body to excrete half of the radioisotope. The effective half-life is the time required for the amount of a radioisotope in the body to be reduced to half its original amount, as a result of both decay of the radioisotope and its excretion.