Answer:
4(19x + 42n + 15)
Explanation:
Devi bought 7 skirts at $x each, n skirts at $12 each, (2n + 1) skirts at $15 each and 4 skirts at $3x each. Find the total cost of the skirts she bought. 
 
total cost of the skirt bought can be determined by adding the total costs of each shirt bought 
 7 skirts at $x each = $7x 
 n skirts at $12 each = $12n 
 (2n + 1) skirts at $15 = (2n + 1) x 15 = 30n + 15 
 4 skirts at $3x each = $12x 
 7x + 12n + 30n + 15 + 12x 
 combine like terms 
 19x + 42n + 15