Let the total number of sweatshirts sold be S and the total number of baseball caps sold be B
Total sales is the total number of sweatshirts sold times $20 plus the total number of baseball caps sold times 10. 
Equation 1: 20S + 10B = 2860
people bought 6 times as many sweatshirts as caps. Which means the number of sweatshirts sold (S) is 6 times caps sold(B) 
Equation 2:  S = 6B — substitute S in equation 1 with 6B
=> 20(6B) + 10B = 2860
=> 120B + 10B = 2860
=> 130B = 2860 — divide both side by 130 
=> B = 2860/130 
=> B = 22 — is the number of caps sold. 
To find the number of sweatshirts sold we use equation 2
S = 6B — but we know now B = 22
=> S = 6(22) 
=> S = 132 

therefore 132 sweatshirts sold and 22 baseball caps sold.