To solve 1-3 you just take the percent and divide it by 100. Ex: 57%/100 = 0.57. Then you take that number and multiply it by the cost of it. Ex: 0.57 * 899 = 512.43. 512.43 is 57% of 899. I hope this helps :)
Your linear function is in the slope-intercept form of a line, y = mx + b, where m is the value of the slope, and b is the value of the y-intercept. The number in the m position in your equation is 1/6, and thee number in the b position in your equation is 7. So the second choice is the one you want.