Answer:
She must score an 8.8 or higher
Step-by-step explanation:
The average is the sum of the number divided by the number of numbers
Let x be the score on the 4th dance
The average is
( 8.9+7.1+ 9.2+x)/4
This must be at least 8.5
( 8.9+7.1+ 9.2+x)/4≥ 8.5
Multiply by 4
( 8.9+7.1+ 9.2+x)/4*4≥ 8.5*4
( 8.9+7.1+ 9.2+x)≥ 34
Combine like terms
( 25.2+x)≥ 34
Subtract 25.2 from each side
( 25.2-25.2+x)≥ 34-25.2
x≥ 8.8
She must score an 8.8 or higher