Marquis wrote the linear regression equation y=1.245x - 3.684 to predict the cost, y, of x songs purchased. marquis spent $40 on songs. which is the best estimate of the number of songs that marquis purchased?

What you should do for this casp is to use the given expression and clear the value of x.
 We have then:
 y = 1.245x - 3.684
 Clearing x:
 1.245x = (y + 3.684)
 x = (y + 3,684) / (1,245)
 Substituting the value of y:
 x = ((40) +3,684) / (1,245) = 35.09
 x = 35
 
 the best estimate of the number of songs that Marquis purchased is 35