We can set up an equation to find Mr. Flynn's height:
$$
\text{Height} = 90 + \frac{\text{Height}}{2}
$$
To solve for the height, multiply both sides of the equation by 2:
$$
2 \times \text{Height} = 180 + \text{Height}
$$
Subtract $\text{Height}$ from both sides:
$$
\text{Height} = 180 , \text{cm}
$$
So Mr. Flynn is 180 centimeters tall