How much does one loaf of bread cost?

One loaf of bread and six rolls cost $1.80. At the same prices, two loaves of bread and four rolls cost $2.40. How much does one loaf of bread cost?

Let B represent the cost of one loaf of bread and R represent the cost of one roll.

1B+6R=$1.80 = 180 cents ------(1)
2B+4R=$2.40 = 240 cents ------(2)

(1) * 2 gives
2B+12R=360 ----(3)

(3)-(2) gives
12R-4R=360-240
8R=120
R=15

B=180-6R=180-6*15=180-90=90

One loaf of bread costs 90 cents.