to get the answer simply substitute the given value to the given equation
after substituting the value, instead of f(a) it will then become f(-a)
change the value of every "a" in the equation according to the given; which is -a.
after substituting the given the answer will become f(-a) = -2a^2 - a
solution:
f(a) = 2a^2 + a if f(-a)
f(-a) = 2(-a)^2 +(-a)
f(-a) = -2a^2 - a from addition the operation became subtraction because in math (+)(-) = (-) "positive time negative is negative".