Hello.
The answer
x in (-oo:+oo)
(1/5)*(2*x-15)+(3/5)*x = 1-4+4 // - 1-4+4
(1/5)*(2*x-15)+(3/5)*x-4-1+4 = 0
1/5*(2*x-15)+(3*x)/5-4-1+4 = 0
(1/5*5*(2*x-15))/5+(3*x)/5+(-4*5)/5+(-1*5)/5+(4*5)/5 = 0
1/5*5*(2*x-15)+3*x-4*5-1*5+4*5 = 0
5*x-20-15-5+20 = 0
5*x-35-5+20 = 0
5*x-40+20 = 0
5*x-20 = 0
(5*x-20)/5 = 0
(5*x-20)/5 = 0 // * 5
5*x-20 = 0
5*x-20 = 0 // + 20
5*x = 20 // : 5
x = 20/5
x = 4
Have a nice day