1.255 times the party bill. x = party bill s = sales tax t = tip C = total cost = the bill, plus the sales tax, and the tip C = x + s + t We know that both the sales tax and the tip are percentages based on the party bill. The sales tax is equal to 7.5% of the party bill. The tip is equal to 18% of the party bill. so, s = (0.075)*x and, t = (0.18)*x Then we replace the s and the t in our equation, C = x + 0.075x + 0.18x Then, we add the elements together. C = (1+0.075+0.18)x C = 1.255x