Эти уравнения решаются пропорцией.
1) (х-213)/(43+17)=100
x-213 = 100*(43 + 17)
x-231 = 100* 60
x-231 = 6 000
x = 6 000+231
x = 6 231
2) (2 500+х)/(83+17) =43
2 500+х = 43*(83+17)
2 500+х = 43*100
2 500+х = 4 300
x = 4 300-2 500
x = 1 800
3) (х+17)/(25+957)=57
х+17 = 57*(25+957)
х+17 = 57*982
х+17 = 55 974
x = 55 974-17
x = 55 957
4) (х+101)/(93+28)=289
х+101 = 289*(93+28)
х+101 = 289*121
х+101 = 34 969
x = 34 969-101
x = 34 868