For what values of a and b will the following system of linear equations has infinitely many solutions ? 21 - 3y = 7 ; (a+b)x - (a +b -3)y = 4a+b​

Rob spent 25%, percent more time on his research project than he had planned. he spent an extra h hours on the project. which of the following expressions could represent the number of hours rob actually spent on the project? two answers