here t1/t2=t3/t4
and t2 is a prime no let be that be y and t1 be x so t1/t2=x/y since t3/t4=t1/t2 so t3=x*k and t4= y*k so we can say that t5 will be x*k2 and t6= y*k*k
so anwer will be a prime no * a square and only 28 fits into that=7*2*2
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