Let
x--------------> total volume of a glass
we know that
(4/7)x-70=(2/4)x------------> (4/7)x-70=(1/2)x--------> 2*(4/7)x-2*70=x
(8/7)x-140=x
multiplied by 7 the expresion
7*(8/7)x-7*140=7*x-----------> 8x-980=7x--------> x=980 cm³
the answer is
the total volume of the glass is 980 cm³
