Explanation:
substitution means to use one equation to express one variable only in terms of the other variable and constants.
let's use
6f + 11b = 317
for that purpose.
6f = 317 - 11b
f = (317 - 11b)/6
now we use that my substituting "f" by its identical expression in b in the second equation :
7(317 - 11b)/6 + 5b = 221
to avoid handling fractions we multiply everything by 6 :
7(317 - 11b) + 30b = 1326
2219 - 77b + 30b = 1326
893 - 47b = 0
893 = 47b
b = 893/47 = 19 cents
f = (317 - 11b)/6 = (317 - 11×19)/6 = (317 - 209)/6 =
= 108/6 = 18 cents
a piece of fudge is 18 cents.
a piece of bubble gum is 19 cents.