> restart:s1:=subs(x=2.3,A*x^4+B*x^3+C*x^2+D*x+F-3.57);

s1 := 27.9841*A+12.167*B+5.29*C+2.3*D+F-3.57

> s2:=subs(x=4.5,A*x^4+B*x^3+C*x^2+D*x+F-2.35);

s2 := 410.0625*A+91.125*B+20.25*C+4.5*D+F-2.35

> s3:=subs(x=5.32,A*x^4+B*x^3+C*x^2+D*x+F-6.21);

s3 := 801.0258458*A+150.568768*B+28.3024*C+5.32*D+F...

> s4:=subs(x=21.3,A*x^4+B*x^3+C*x^2+D*x+F-5.22);

s4 := 205834.6161*A+9663.597*B+453.69*C+21.3*D+F-5....

> s5:=subs(x=12.37,A*x^4+B*x^3+C*x^2+D*x+F-8.73);

s5 := 23414.17169*A+1892.819053*B+153.0169*C+12.37*...
s5 := 23414.17169*A+1892.819053*B+153.0169*C+12.37*...

> fsolve({s1,s2,s3,s4,s5},{A,B,C,D,F});

{B = -.5604767715, A = .1357969533e-1, D = -31.5693...
{B = -.5604767715, A = .1357969533e-1, D = -31.5693...

> Sol:=subs(%,A*x^4+B*x^3+C*x^2+D*x+F);

Sol := .1357969533e-1*x^4-.5604767715*x^3+7.1723447...
Sol := .1357969533e-1*x^4-.5604767715*x^3+7.1723447...

> subs(x=4.5,Sol);

2.34999991

>