For part A: the constant is 83.50. the variable would be c and w. and the coefficient would be 10c or 15w.
part B: so 10(4)+15(15)+83.50 -----> 10x4= 40------> 40+15(15)+83.50---->15x15=225 40+225+83.50=348.50
part C The coefficient would change because a constant is always constant, a variable is just a letter standing in for a number which would make the coefficient the one that changes for $10 to $20. hope that help!