# Mathemetical operation with two imageCollections

I try to find relative humidity (RH), I created two different imagecollections (please see: 'ue' and 'ues'). Now I want to do RH= '100 * ue / ues' mathematical operation with these two image collection. Can anyone help me?

``````var ROI = table.filter(ee.Filter.eq('ADM1_NAME', 'Varna'));

var collection = ee.ImageCollection("ECMWF/ERA5_LAND/MONTHLY_AGGR");
var filteredCollection = collection.filterDate('2018-01-01', '2019-01-01').filterBounds(ROI);
print('filteredCollection',filteredCollection)

//
var T0 = 273.16;

// vapor pressure for air temperature
function es(image){
return image.expression('611.21 * exp(17.502 * (T - T0) / (T - 32.19))', {
'T': image.select('temperature_2m'),
'T0': T0
}
).set('system:time_start', image.get('system:time_start'));
}

var ues=filteredCollection.map(es);
print('ues',ues)

// vapor pressure for dew point temperature
function e(image){
return image.expression('611.21 * exp(17.502 * (Td - T0) / (Td - 32.19))', {
'Td': image.select('dewpoint_temperature_2m'),
'T0': T0
}
).set('system:time_start', image.get('system:time_start'));
}

var ue=filteredCollection.map(e);
print('ue',ue)
``````

No need to do it in two steps, just use one function:

``````function vp(image){
var ues =  image.expression('611.21 * exp(17.502 * (T - T0) / (T - 32.19))', {
'T': image.select('temperature_2m'),
'T0': T0
}
)
var ue = image.expression('611.21 * exp(17.502 * (Td - T0) / (Td - 32.19))', {
'Td': image.select('dewpoint_temperature_2m'),
'T0': T0
}
)