Kai is buying boxes of cookies at a bakery. Each box of cookies costs \$4$4dollar sign, 4. He wrote this equation to find how many dollars he'll spend (d)(d)left parenthesis, d, right parenthesis when he buys some number of boxes of cookies (c)(c)left parenthesis, c, right parenthesis:
d=4cd=4cd, equals, 4, c
Identify the dependent and independent variables.