var rachunkiOli = [105, 30, 74, 221, 155];
for (var i = 0; i < rachunkiOli.length; i++) {
var napiwek;
if (rachunkiOli[i] <= 50 ) {
napiwek = rachunkiOli[i] * 0.2;
} else if (rachunkiOli[i] > 50 && rachunkiOli[i] <= 150) {
napiwek = rachunkiOli[i] * 0.15;
} else if (rachunkiOli[i] > 150) {
napiwek = rachunkiOli[i] * 0.1;
}
}