Help with a Postgres Function

I have a function which I need amending to take in and use two additional parameters. CREATE OR REPLACE FUNCTION boundaries.usp_drivingrange_stz(source integer, drivetime integer) RETURNS geometry LANGUAGE plpgsql AS $function$ DECLARE retRange geometry:=null; BEGIN SELECT st_multi(st_buffer(st_collect(geom_way),.00008)) into retRange FROM "UKRoads".node as node JOIN (SELECT * FROM pgr_drivingDistance(' SELECT [login to view URL], [login to view URL], [login to view URL], h.cost_m + COALESCE(a.add_cost_m, 0) + COALESCE(b.add_cost_m, 0)::real AS cost, h.reverse_cost_m + COALESCE(a.add_cost_m, 0) + COALESCE(b.add_cost_m, 0)::real AS reverse_cost FROM hh_2po_4pgr h LEFT JOIN (select id, add_cost_m from additional_costs_a where delay = 10) as a ON [login to view URL] = [login to view URL] LEFT JOIN (select id, add_cost_m from additional_costs_b where delay = 5) as b ON [login to view URL] = [login to view URL]', source, drivetime, false)) AS dd ON [login to view URL] = [login to view URL]; RETURN retRange; END; $function$ ; I want the 10 and the 5 used in the two joins below to be taken from parameters to the function. LEFT JOIN (select id, add_cost_m from additional_costs_a where delay = 10) as a ON [login to view URL] = [login to view URL] LEFT JOIN (select id, add_cost_m from additional_costs_b where delay = 5) as b ON [login to view URL] = [login to view URL]',