can someone explain me the qn 11 in R-1 class qns in beckers.

I dint get the explaination.

if someone cud xplain me with example wud be grt

I dint understand "If the taxpayers combined income(AGI(+) iNT ON TAX EXEMPT BONDS (+) 50% OF SOCIAL SECURITY BENEFITS), is below the threshhold amt then

doubt  how is the taxable amt lesser of

(1) 50% of benefits

           OR

(2) 50% of excess of combined income over threshold amt?? (if the amt is less than the threshhold amt then how can there be a excess??????)