Question 185146
solution:
 let x be the number of adult attented
 let y be the number of children attended

 given:
  cost of adult = $2.00
  cost of child = $1.50

 x + y = 578            (equation 1)
 2.00x + 1.50y = 985  (equation 2)

 x + y = 578 => x = 578 - y (equation 3)

 2.00(578 - y) + 1.50y = 985 (substituting the value of x in eq. 1 to eq. 2)
 1156 - 2.00y + 1.50y = 985
 -2.00y + 1.50y = 985 - 1156
 -0.50y = -171 (diving both sides by -0.50)
 y = 342

 x = 578 - y (eq. 3)
 x = 578 - (342) (substituting the value of y which is 342))
 x = 236

therefore, the number of adults attended the concert was 236 and the number of children attended was 342...