If st=13 and rs=16 then rt = ?

Solve for r and t

st=13

divide by s

t=13/s

rs=16

solve for r

divide by s

r=16/s

so rt = (13/s) (16/s) = (208) / (s^2)

If these are whole numbers, then st=13 means that either s=1 and t=13 or s=13 and t=1.

rs = 16 means that s is a divisor of 2, and s=13 won't work, so s must be 1 and t=13.

Since s=1 and rs=16, r = 16/s = 16

So rt = (16) (13) = 208

If these are not whole numbers, then the other answers have shown you that rt=208/s² can be any positive number. (If complex numbers are allowed, then rt can be any nonzero number, real or complex.)