Explanation:
you need help with that in what way ? it is all plainly written there already.
don't shut off your brain and common sense, just because it is math. you can solve math problems with common sense way more often than people tend to think.
common sense IS logic ...
so, "to solve f(x) = -78.8" simply means, we need to find every value of x for which f(x) = -78.8
looking at the table :
how often do we find -78.8 under f(x) ?
aha ! 1 time, right in the first line.
what is the value of x for this table item ?
well, the x values in the table are on the left side, so, we take the value to the left of -78.8.
and that is ... 0.
so, the solution is x = 0 or simply 0.
that really was it.