he didn’t combine the -5r + 4r correctly and also he didn’t multiply 4 and -5 correctly.
if you can show your work. use
F O I L method
first
outer
inner
last.
r • r = r^2
r • -5 = -5r
r• 4 = 4r
4• -5 = -20.
the final equation is
R^2 + r -20