Can someone help, I don't get the question

Step-by-step explanation:
f(n) = (-5). f(n-1) +15
f(1) = 3
for n = 2
f(2) = (-5).(3)+15 = -15+15 = 0
for n = 3
f(3) = (-5).0 +15 = 0+15 = 15
for n = 4
f(4) = (-5).(15) + 15 = -75 +15 = -60
so, the sequences are :
3, 0, 15, -60
[tex]\\ \sf\longmapsto f(n)=(-5)f(n-1)+15[/tex]
Here
[tex]\\ \sf\longmapsto D_f=(0,\infty)[/tex]
[tex]\\ \sf\longmapsto f(1)=3[/tex]
[tex]\\ \sf\longmapsto f(2)=(-5)f(1)+15=(-5)(3)+15=-15+15=0[/tex]
[tex]\\ \sf\longmapsto f(3)=(-5)(0)+15=0+15=15[/tex]
[tex]\\ \sf\longmapsto f(4)=(-5)(15)+15=-75+15=-60[/tex]