Answer is B
Here, there nothing specified about how we access memory when there is a miss in cache,
So we take Default case
formula: (Memory access time wiithout cache) = (main memory time).
formula: (memory access time with cache) = hit(cache time) + miss(Main memory time)
In this problem.. cache time= 10ns and memory access time with cache =20ns and main memory time=110ns
so simply put the values in formula
20 = h(10)+(1-h)(110)
so we will get h=0.9
and hence answer is (B)=90%