[etc]

var l = 0;
var r = 0.015;
var z = 1.3;
var k = 2.2;
var m = 2.6;
but.onPress = function() {
	if (v.selected == true) {
		z = 2.2;
	} else {
		z = 1.3;
	}
	txt.text = r*z*l;
};

Оно?