Final answer:
To find an expression with a value of 20, we reviewed a quadratic equation, but it would not directly provide the value without solving for a variable. The electron configuration for an atom with 20 electrons is for calcium, which is indeed an expression with a fixed value, but related to chemistry rather than an arithmetic value.
Step-by-step explanation:
The question asks for an expression that has a value of 20. Among the multiple expressions provided, let's consider the quadratic equation mentioned in the prompt which is of the form at² + bt + c = 0. The coefficients provided in one scenario are a = 4.90, b = -14.3, and c = -20.0. When these values are substituted into the quadratic formula, we can find the values of 't' that would satisfy the equation:
Quadratic formula: t = (-b ± √(b² - 4ac)) / (2a)
To see if this relates to our search for the expression with a value of 20, we need to determine if the solution for 't' would indeed give us 20 when substituted back into the original equation. However, since the question asked specifically for an expression that equals 20, without solving for a variable, this quadratic equation would not be the correct choice as it does not immediately offer a value of 20 without further calculation.
Among the options listed, we do not have enough information to conclude which one has a value of 20 without more context or calculations. However, it's worth noting that the electron configuration of an atom with 20 electrons is for the element calcium (Ca), which is 1s² 2s² 2p¶ 3s² 3p¶ 4s².