Im having arithmetic question problem

the question is -
the sum of the first 4 terms of an arithmetic series is -8 and the sum of the first 5 terms is 85. determine the first erm and the common difference.

i honestly have no idea what to do..

a1+a2+a3+a4 = -8
a1+a2+a3+a4 +a5 =85

==> a5= 85- -8= 93

a1
a2=a1+d
a3=a1+2d
a4=a1+3d
a5=a1+4d

S(4)= a1+a1+d+a1+2d+a1+3d= -8
S(5)= a1+a1+d+a1+2d+a1+3d + a1+ 4d = 85

simplify them, you have two equations and two unknowns a1 and d
use elimination or substitution method , solve for a1 and d