In the given equation, is a coefficient and y is the variable.
coefficient is a constant number or quantity multiplied to a variable in an algebric expression. Like in the above equation is a coefficient and y is the variable. We use term variable for y as its value may vary or change. If variable does not have any coefficient in any expression then in that case, we consider 1 as coefficient, for example: , here variable have 1 as coefficient.
The original price is c. Then the grocery bill will be: c - 0.05c = 0.95 c. You can also say since the beggining that 5% disscount implies 0.95 factor, which leads to c * 0.95 = 0.95c. Sorry if it’s wrong