Question 1154218

 {{{1.3s+1.7f=37.9}}}......eq.1
{{{5.4s+5.6f=147.2}}}.....eq.2
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start with

{{{1.3s+1.7f=37.9}}}......eq.1, solve for {{{s}}}

{{{1.3s=37.9-1.7f}}} 

{{{s=37.9/1.3-1.7f/1.3}}}

{{{s=29.15-1.308f}}}........a)

substitute in eq.2

{{{5.4(29.15-1.308f)+5.6f=147.2}}}.....eq.2,  solve for {{{f}}}

{{{157.41 - 7.0632f+5.6f=147.2}}}

{{{157.41 - 1.4632f=147.2}}}

{{{157.41 -147.2 = 1.4632f}}}

{{{10.21 = 1.4632f}}}

{{{f=10.21/1.4632}}}

{{{f=6.98}}} ≈{{{7}}}

go to

{{{s=29.15-1.308f}}}........a), substitute {{{f}}}

{{{s=29.15-1.308*6.98}}}

{{{s=29.15-9.12984}}}

{{{s=20.02}}}≈{{{20}}}