$7.79 = p number of pennies worth $.01 each, n number of nickels worth $.05 each, d number of dimes worth $.10 each, and q number of quarters worth $.25 each. p = n = d = q
Algebraically, this is written:
7.79 = .01p + .05n + .10d + .25q
Since there is the same number of each type of coin, the variables are all equal to each other. This means that they can all be referred to as 'x'.
7.79 = .01x + .05x + .10x + .25x = .41x
7.79 = .41x
.41 = .41
19 = x