j=jack's age
s=susan's age
ok so
jack is 27 years more than susan
j=27+s
in 5 years (j+5 and s+5), he (jack in 5 years) will be (=) 4 times as old as hwer (susan in 5 years)
j+5=4(s+5)
so we have
j=27+s and
j+5=4(s+5)
subsitute 27+s for j since they are equal
27+s+5=4(s+5)
distribute
a(b+c)=ab+ac
4(s+5)=4s+20 so we have
27+s+5=4s+20
add like terms
32+s=4s+20
subtract s from both sides
32=3s+20
subtract 20 from both sides
12=3s
divivde 3
4=s
subsitute
j=27+s
j=27+4
j=31
jack is 31
susan is 4