How to calculate and assign to variables directly in memory?

[#1]

For example: the number of height and weight that meet the conditions at the same time

Thanks!

[#2]

dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
s = Sum( dt[0, "height"] < 60  dt[0, "weight"] < 90 );

//s=5

？？

[#3]

I SEE

dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
s = Sum( dt[0, "height"] < 60  (dt[0, "weight"] < 90) );