jmc

Suppose that a taco costs $t$ dollars and and enchiladas cost $e$ dollars each. Then the given information implies that $2e+3t=2.50$ and $3e+2t=2.70$. Multiplying the first equation by 3 yields $6e+9t=7.50$, and multiplying the second equation by 2 gives $6e+4t=5.40$. Subtracting these two equations, we see that $5t=2.10$. Thus one taco costs $\frac{2.10}{5}=.42$, and two tacos are $.84$. Since we are given the price of three enchiladas and two tacos, we see that three enchiladas and four tacos total 2.70 + .84 = \boxed{\3.54}$.