SOLUTION: Please solve Using Substitution: {{{7s+5t=13}}} {{{3t-s=-13}}}

Algebra ->  Expressions-with-variables -> SOLUTION: Please solve Using Substitution: {{{7s+5t=13}}} {{{3t-s=-13}}}      Log On


   

Question 243956: Please solve Using Substitution:
7s%2B5t=13
3t-s=-13
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
Please solve Using Substitution:
7s+5t=13
3t-s=-13
solve second for s
add 13 and s to both sides
3t+13=s
substitute s into first
7* (3t+13)+5t=13
21t+7*13+5t=13
combine
26t+7*13=13
divide by 13
2t+7=1
subtract 7 from both sides
2t=-6
t=-3
substitute t into second equation
why second?
it is easier to multiply and divide
3*(-3)-s=-13
-9-s=-13
multiply both sides by -1
9+S=13
s=4
and t=-3
check
7s+5t=13
7*4+5*(-3)=13
28-15=13
13=13
ok