Explanation:
then let's transistors this into mathematical symbols :
9 times a number y
9×y or simply 9y
subtracted from 85
85 - ...
is seven times
= 7 × ...
the sum of four and y
(4 + y)
together this is then
85 - 9y = 7 × (4 + y)
and just FYI : let's solve this
85 - 9y = 7×4 + 7y = 28 + 7y
85 = 28 + 16y
57 = 16y
y = 57/16 = 3.5625