For equal roots, discriminant should be zero.
Given equation: 3x2−kx+3=0
Compare above equation with general form ax2+bx+c=0 , we get
a=3,b=−k,c=3
So discriminant, D=b2−4ac=0
⇒b2−4ac=0
⇒k2−4(3)(3)=0
⇒k2=36
⇒k=6 or −6
Since, we have to find only positive value of k
Hence, value of k is 6