Problems don't equal numbers, although their solutions usually do.
There are an infinite number of multiplications whose products are 91.
Here are a few:
91
91 * 13 = 1,183
91
45 + 46 = 91.
There are 100 centimetres in 1 metre so 91 centimetres is equal to 0.91 metres.
91/100
1 x 91, 7 x 13.
99.519 yards = 91 meters
7 x 13 = 91.
13
There are 10 millimetres in one cetnimetre. Therefore, 91 millimetres is equal to 91/10 = 9.1 centimetres.
91. Atomic number is equal to the number of protons.