Strategy: The conjugate acid should have one extra proton in each case.
Solution: `NH_2^(-)(aq.)+H^(+)(aq.)rarrunderset("Conjugate acid")(NH_3(aq.))`
`NH_3(aq.)+H^(+)(aq.)rarrunderset("Conjugate acid")(NH_4^(+)(aq.))`
`HCOO^(-)+H^(+)rarrunderset("Conjugate acid")(HCOOH)`