-158 : -90=

To solve the expression \(-158 : -90\), you divide \(-158\) by \(-90\).

\[ -158 \div -90 = \frac{158}{90} \]

Now, simplify the fraction:

\[ \frac{158}{90} = \frac{79}{45} \quad \text{(since both 158 and 90 can be divided by 2)} \]

Thus,

\[ -158 : -90 = \frac{79}{45} \]

So, the answer is \(\frac{79}{45}\) or approximately \(1.7556\) when expressed as a decimal.