Biconditional is an operation on two logical values, typically the values of two propositions, that produces a value of true if and only if both operands are false or both operands are true.
Making pairs by R as follows
If 6s 7 = 8, then 2r = -2.
If 2r= -2, then 6s+ 8 = -7.
If 6s+ 8 = -7, then 2r = 0.
If 2r= 0, then 6s - 7 = 8.
If 8s + 6 = -7, then 2r2 = 0.
If 2r2 = 0, then 8s + 6 = -7.
checking the pairs by s to see where we can form a biconditional
If 6s 7 = 8, then 2r = -2.
If 2r= -2, then 6s+ 8 = -7.
Not biconditional
If 6s 7 = 8, then 2r = -2.
If 2r= -2, then 6s+ 8 = -7.
Not biconditional
If 8s + 6 = -7, then 2r2 = 0.
If 2r2 = 0, then 8s + 6 = -7.
Biconditional
Using options
4 and 5