Sqlite subquery with multiple sums

I have a sqlite database and I need to perform some arithmetic in my sql to get the final amount. The thing is I am not certain how to go and achieve this, I'm pretty certain from what I've been reading its a subquery which I need to group by lineID (unique id in my db)

The fields I want to include in the calculation below are

el.material_cost1 * el.material_qty1
el.material_cost2 * el.material_qty2
el.material_cost3 * el.material_qty3

The query I currently have is below. It returns the value of my costs apart from the fields missing above. As I store the material costs individually, I can't work out how to do a subquery within my query to get the desired result.

SELECT sum(el.enquiry_cost1) + sum(el.enquiry_cost2) + sum(el.enquiry_cost3)
FROM estimate e
LEFT JOIN estimate_line el
ON e.estimateID=el.estimateID
WHERE e.projectID=7 AND el.optional='false'