In case of a TLB hit, memory access time is 230 ns (30 ns to search the TLB and 200 ns to access memory).
In case of TLB miss, memory access time is 430 ns (30 ns to search the TLB to find there is no page entry, 200 ns to first access memory to find the page-frame mapping and then another 200 ns to access the desired byte in memory).
Effective memory access time is obtained by weighted averaging of the two times:
Let $x$ be the TLB hit ratio. Then, $150=x*230+(1-x)*430 \implies 200x=280 \implies x=1.4$
Is the question correct? I think some values are incorrect. Even if we put $x=1$, the best possible EMAT is 230 ns.