If it is two equations then:
c = 150b
c = 200 + b
Is the same as saying:
150b = 200 + b
Subtract b from both sides:
150b - b = 200
Which is the same as:
149b = 200
So
b = 200/149 (or 1.3422818791946308724832214765101 as others said)
Put that value of b back into one of the original equations:
c = 150b
c = 150 * 200/149
c = 30000/149 (or 201.34228187919463087248322147651 in decimal)
You can confirm by inserting both values into the other original equation:
c = 200 + b
30000/149 = 200 + 200/149
30000/149 = 29800/149 + 200/149
All Good!