Approximating another straddle price

By the straddle approximation formula, the ATM straddle price is proportional to the square root of time to expiry, that is: $Y \propto \sqrt{t}$ In the first case, $t = 5$ corresponds to a price of $\text{\$1.30}$ .
In the second case, $t = 20$ is $4$ times as long as before. Quadruple the time to expiry, double the price (since the square root of $4$ is $2$ ). So the answer is $2 \times \text{\$1.30} = \boxed{\text{\$2.60}}$