Chapter 1 - Solving Linear Equations - 1.2 - Solving Multi-Step Equations - Exercises - Page 17: 37

one taco costs $\$3.75$, assuming that the tax was calculated on the pre-tip amount.

$(2t+s)+.08(2t+s)+3=\$13.80$ $s=2.50$ $(2t+2.50+.08(2t+2.5)+3=\$13.80$ $-3$ from both sides $(2t+2.50)+.08(2t+2.5)=\$10.80$ $(2t+2.50)+.16t+.2=\$10.80$ $-.2$ from both sides $(2t+2.50)+.16t=\$10.60$ $-2.5$ from both sides $2t+.16t=\$8.10$ Combine like terms $2.16t=\$8.10$ $t=\$3.75$