What is the molecular weight limit $(M_c)$ for mixing $SP\frac{B}{d}SPB$ at $25C$ and obtaining one phase?

Assume both polymers have the same density, molecular weight, and repeating molecular weight

of $100\frac{g}{m}ol$ for both polymers, and they are mixed at a $1$:$1$ ratio. Use the A and B values from

problem #$4.$ Report both the $N_c$ and $M_c$ values. Show your work and first derive an equation to

calculate $N_c.$