Answer:
85,999,999.999 999 909
Explanation:
The expression represents the difference of a relatively large number and one that is relatively small. That difference is approximately the value of the large number. The exact value requires 17 digits for its proper expression. Most calculators and spreadsheets cannot display this many digits.
Standard form
The numbers in standard form are ...
86,000,000 = 8.6×10^7
0.000000091 = 9.1×10^-8
Difference
Their difference is ...
86,000,000 -0.000000091 = 85,999,999.999 999 909
In scientific notation, this is ...
8.599 999 999 999 990 9×10^7