Question

Does anyone know how to solve 81 increased to 90?

Answer 1

That seems an odd way of wording the question. Do you mean 81+x=90? In other words, what number can you add to 81 to get 90. You can also switch it around so 90-81=x.

81+x=90
x=90-81
x=9

Answer 2

89+90=171. keep in mind that increased or increased by means to add