filtering a row of a jagged array

[DanielG]

int[][] whatever = [
     [0],
     [0, 1, 2],
     [5, 6, 7, 8, 9, 10]
];
writeln(whatever[2]);                    // [5, 6, 7, 8, 9, 10]
writeln(typeid(whatever[2]));            // int[]
auto x = whatever[2].filter(x => x > 7); // error

Error: template std.algorithm.iteration.filter cannot deduce 
function from argument types !()(int[], void), candidates are: ...

Online example:
https://run.dlang.io/is/LUXFuF

...

I'm guessing I need to give the compiler some help understanding 
that this is an array of ints, but 1) how, and 2) why? [if 
typeid() seems to understand just fine?]